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Development of hygienic features in dishwashers - Disinfection by the use of UV-light and Ozone

LINUS ÅBERG

Master of Science Thesis Stockholm, Sweden 2008

Development of hygienic features in dishwashers - Disinfection by the use of UV-light and Ozone

Linus Åberg

Master of Science Thesis MMK 2008:9 MCE158 KTH Industrial Engineering and Management

Machine Design SE-100 44 STOCKHOLM

Examensarbete MMK 2008:9 MCE158

Utveckling av hygienfunktioner i diskmaskiner – Desinfektion med hjälp av UV-ljus och ozon

Linus Åberg

Godkänt

2008-02-19

Examinator

Lars Hagman

Handledare

Conrad Luttropp Uppdragsgivare

AB Electrolux Kontaktperson

Elisabetta Bari

Sammanfattning Detta examensarbete inom inriktningen Integrerad Produktutveckling på KTH, utfört på Primary Development Dishcare på AB Electrolux syftar till att utveckla lösningar för att öka det hygieniska resultatet i diskmaskiner. Resultaten av detta arbete är funktionsprototyper för att undersöka användningen av UltraViolett ljus och ozon i diskmaskiner.

Arbetet har följt Electrolux Primary Development process, med leverabler och checkpoints.

Ultraviolett ljus med en våglängd på 264 nm går igenom cellväggar på bakterier och mikroorganismer och förändrar cellernas DNA. Detta hindrar bakterien från att föröka sig och ses då som död. Vanligtvis används UV-C-lampor med en våglängd på 254nm, vilket är väldigt nära den optimala våglängden för att döda bakterier.

En konkurrent till Electrolux har nyligen lanserat en diskmaskin som hävdas nå ett högre hygieniskt resultat med hjälp av en UV-lampa. Denna testades under examensarbetet och fanns ha en väldigt låg påverkan på det hygieniska resultatet.

Två prototyper utvecklades och testades med avseende på UV- desinfektion av diskgods. Dessa visade att UV bara kan desinficera ytor som får en direktträff av UV-strålningen. Detta gör en UV-lampa svår att implementera i en diskmaskin på grund av det komplexa arrangemanget av diskgods. Däremot kan en UV-implementering öka det upplevda hygieniska resultatet och på så vis användas som en marknadsföringsfunktion.

Även ozon kan användas för att eliminera mikroorganismer i luft och vatten, ett flertal möjligheter kan ses. Det kan exempelvis vara möjligt att spara vatten från den sista sköljningen och behandla vattnet med ozon eller UV-ljus för att förhindra bakterietillväxt. Även vattnet som används under diskcykeln skulle kunna desinficeras och på så sätt minska behovet av diskmedel.

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Master of Science Thesis MMK 2008:9 MCE158

Development of hygienic features in dishwashers - Disinfection by the use of UV-light

and Ozone

Linus Åberg

Approved

2008-02-19 Examiner

Lars Hagman Supervisor

Conrad Luttropp Commissioner

AB Electrolux Contact person

Elisabetta Bari

Abstract

This thesis within the field of Integrated Product development at the Royal Insitute of Technology, performed at Primary Development Dishcare at AB Electrolux, is supposed to find a solution to enhance the hygiene inside an Electrolux dishwasher. The outcomes of this thesis are functional prototypes to evaluate the efficiency of disinfection by the use of Ultra Violet Light and Ozone.

The thesis has followed Electrolux Primary Development process, with delivarables and checkpoints.

Ultra violett light with a wavelength of around 264 nm penetrates through the cell wall of bacteria and micro organisms and causes a molecular rearrangement of the cells DNA. This prevent the bacteria from reproducing and it is considered dead. Commonly used UV-C lamps transmits the wavelength 254 nm which is very close to the optimum for germicidal action.

A competitive brand have reacently launched a dishwasher claiming to achieve greater disinfection with an UV feature. This dishwasher was tested during the thesis and proven to have a very low effect on the hygienic result.

Two prototypes were devolped and tested for UV disinfection of dishware. It was found that UV will only kill bacteria that is in direct contact with the UV irradiation. This makes an UV feature unfeasible for a dishwasher due to the complex arrangement of dishware. However may an UV feature enhance the percieved hygienic result of the dishwasher and therefore act as a marketing feature.

Ozone can also be used for killing micro-organisms in air and water, several possibilities can be seen. It could be possible to save water from the last rinse and treat it with ozone or UV to prevent bacteria growth. The water may also be treated within the dishcycle and therefore decrease the need of detergent.

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Acknowledgements The work has been very interesting and instructive, with a great variety of tasks. The experiences of having worked in an international environment with very skilled people in one of Swedens biggest companies, as well as having witnessed true product development with state of the art technology have been fascinating in many ways.

Persons that have helped out and supported during the work and who deserves a special acknowledgement are:

Girish Pimputkar, Niklas Olson, Sarah Förster, Per-Erik Pers, Christine Gall, Monica Celotto, Berndt Krische, Claudio Paschini & Industrial Design Team.

And in particular my two instructors Elisabetta Bari at Electrolux and Conrad Luttropp at Department of Machine Design, KTH.

A special acknowledgement is reserved for thesis student Jonas Pettersson, who from the beginning should have been a part of this thesis work, but circumstances during the work changed that. Instead he has been a great support and been counterpart in numerous discussions regarding hygiene in dishwashers.

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Terminology In the report different terminology is used when describing a methods abilities, Hygiene, Cleaning, Disinfection Sanitization and Sterilization, are terms used and in need of a clear definition.

Cleaning Physical method of removing dirt and biological material

Hygiene Maintenance of health and healthy living

Disinfection Killing of pathogenic1 micro-organisms

Sanitization Reduction of germs by at least log 2 (99% kill rate)

Sterilization Killing of all micro-organism

Commonly used abbreviations DW Dishwasher

IDC Industrial Design Centre

CTI Core Technology & Innovation

UV Ultra Violet

PMF Product Management Flow

PPI Primary Project Initiation

PCP Primary Check Point

R&D Research & Development

1 A descriptive term for a thing or condition that can cause disease

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Table of Contents 1 Introduction 1 1.1 Background 1

1.2 Purpose 1 1.3 Targets 2 1.4 Scope definition 2 1.5 Method 2

2 The Electrolux company 5 2.1 Primary Development – prior to product development 5

3 Dishwasher technology 7 3.1 Dishwashers in general 7 3.2 The dishwashing process 11

4 Disinfection methods 13 4.1 UV-C light for disinfection 13 4.2 Other methods for disinfection 18

5 Different brands and their Hygienic features 21 5.1 AEG & Electrolux 21 5.2 Miele 21 5.3 Bosch 23 5.4 Siemens 23 5.5 Whirlpool 23 5.6 Maytag 24 5.7 LG 26

6 Other products using UV for disinfection 29 6.1 UV-C light disinfection applications 29

7 Test of LG UV feature 31 7.1 LG Conclusion 33

8 Creations of ideas 35 8.1 Opportunities and ideas 35 8.2 Idea creation and concept generation 36 8.3 Selection 37 8.4 Patent search 38

9 UV Solution and verification 39 9.1 Electrical circuit and component theory 39 10 Tests of UV abilities 43

10.1 Disinfection tests 43 10.2 Visual tests 45 10.3 Investigation of effects of UV on plastic material 46

11 Concepts 47 11.1 Lamp armatures 47 11.2 Flip down item holder 48

12 Hardware and Solutions 49 12.1 Solution design 49 12.2 Prototypes 49 12.3 Feature visualization 52 12.4 UV Conclusions 53

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13 Ozone in a dishwasher 55 13.1 Ozoniser for odour removal 55 13.2 Ozone in water 57 13.3 Ozone leakage 59

14 Discussion and conclusions 61 14.1 UV feature 61 14.2 Ozone concepts 62 14.3 Process 62

References 63

Appendix 1 – Risk analysis I Appendix 2 – Concepts II Appendix 3 – Evaluation matrixes VII Appendix 4 – Disinfection measurements X Appendix 5 – Bacteria elimination doses XII

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Chapter Overview Chapter 1 describes the thesis purpose, targets and background. Chapter 2-3 describes the company Electrolux and their dishwasher technology. Chapter 4-7 describes disinfection methods together with other brands and products using similar technique. Chapter 8-9 describes the idea creation, concepts generation, selection, patent searches and electrical circuit information regarding the use of UV for disinfection. Chapter 10 present the tests of the UV abilities performed

Chapter 11-12 describes the development of UV-concepts to final prototypes.

Chapter 13 describes several ways to implement Ozone in a dishwasher.

Chapter 14 presents the final discussions and conclusions.

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Development of hygienic features in dishwashers - Disinfection by the use of UV-light and ozone

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1 Introduction This thesis within the field of Integrated Product development, is supposed to result in visible and differentiated solutions that will enhance the hygiene inside a dishwasher.

The thesis is the last step in the Master of Science education at the Royal institute of Technology and performed at Primary Development Dish Care, AB Electrolux.

Market studies have shown that competitors to Electrolux are putting a lot of efforts trying to add hygienic features to their dishwashers in order to increase sales and beat other competitors. Therefore Electrolux wants to investigate what is really working and what would be most suitable to implement in a dishwasher.

The outcomes of this thesis are functional prototypes to evaluate the efficiency of disinfection by the use of Ultra Violet Light and Ozone and a report, describing the methods and results of the pre-study, tests and concept development performed.

Due to competitors use of Ultra Violet light this has been the initial focus of this thesis, followed by an investigation of possibilities with the use of Ozone.

1.1 Background Today environmental and health awareness is increasing, with increasing demands on disinfection as result. In household appliances especially, it has been noticed a significant trend in reassuring the consumers with hygienic features or communication to enhance hygienic performances. In particular considering dishwashers, where the entire machine is built to clean. Competitors to Electrolux are wasting no time marketing their products with high temperature rinses and steam cleaning to communicate a higher grade of disinfection. Therefore, Electrolux wants to evaluate the potential of new technologies of improving hygienic performance of the dishwasher or introducing different way of using it.

Some pre-studies have already been performed, focusing on some well known technologies already used in other industries and sectors to disinfect, in particular referring to Ultra Violet (UV) light. Considering UV technology, the main conclusions for the research done, presented in a technical report[1] are:

• It is believed that this trend will continue

• Hygiene can be used as a sales argument for a lot of products

• It has a potential to improve Dishwashers performances and sales

1.2 Purpose The purpose of the thesis is to investigate technologies and develop new features in order to enhance the hygienic performances of today’s dishwashers, focusing on hygienic result, feasibility and design. The final targets for this thesis are: to prove the advantages of the technology and finalize a prototype providing one differentiated hygienic feature that does not exist on the dishwashers on the market today. Also a written report on the technique of using Ultra Violet light for disinfection, as well as a competitor and market analysis


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1.4 Scope definition The thesis is supposed to focus on implementing solutions of already proven disinfection methods, hygienic features, in a dishwasher. The final solutions will be chosen in order to satisfy structural and operational requirements and/or other constraints of the dishwasher. No bacteriological tests will be performed in order to evaluate the efficiency of the methods, since a specific laboratory setup with bacteria samples is required. That kind of facility is not available in Electrolux, bacteriological tests are usually performed in collaboration with external specialized institutes.

The final task will be to verify that the prototype works properly, and to evaluate with a qualitative approach the efficiency of the method.

Considering a feature using UV technology, the evaluation can be done by measuring the intensity with a UV-meter in the active area identified as the UV-zone, but not perform any laboratory tests with bacteria involved. To do tests with bacteria samples could be the next step for Electrolux, in order to further evaluate the approach.

The task of this thesis is to address consumer needs already identified through dedicated consumer researches. No interviews or surveys, which results in advanced statistics about how people use their dishwasher or what they think about the ideas will be performed, since that is already available. Anyhow, a qualitative feedback on the ideas developed have been done with Electrolux employees and by team members of the Primary development team.

1.5 Method This thesis was from the beginning meant to be performed by two students closely together, but after the pre-study it was clear that the best way to conduct the rest of the work was to separate the remaining work, and write two independent reports. It would have been too much information and a too wide scope, making the report difficult to read, jumping between two focuses to keep it as it was meant originally. The outcome of this split after the pre-study makes the first sections of this report looks the same as the first sections of the other report, focusing on steam.

In order to get an understanding of which methods are possible to use to improve hygiene and kill bacteria in general, a summary of different disinfection methods have been put together. Some of the methods were rather quickly dismissed as inappropriate to use in a dishwasher. The two methods that were found most suitable were to use steam and UV-light to further enhance the hygiene. Those findings were triggers to why the original plan of writing one report was dropped. Both Electrolux and students found it more suitable for all parts to write two separate reports on each disinfection method.

To understand the potential these two technologies and how to use them in dishwashers to enhance the hygiene, a market analysis has been performed by mostly searching on the Internet, in databases and by reading internal reports. Interesting applications have been studied and evaluated if the technique could be transferred to an application in a dishwasher.

In order to know what other dishwasher competitors are doing in this area, a competitor analysis has been performed as well, starting on how different brands market themselves how they communicate around hygiene. Moreover, their hygienic features


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have been analyzed, in order to understand how they work. The analysis has been mostly performed by searching the internet and by reading internal reports.

The idea creation has been going on since day 1, but the methods used to collect ideas from the Primary team and from Industrial designers have been standard Brainstorming sessions, with different focuses. During the work, new ideas have come up all the time as test results indicates new possibilities or proved earlier ideas difficult to implement. The Brainstorming session with the Industrial design team took place at a later occasion than the one with the Primary team. That resulted in some ideas not being evaluated by the same criteria, due to the fact that some tests had been carried out during that time and had generated more knowledge about the problem.

The methods used to evaluate the concepts generated from the Brainstorming session are a decision matrix where some concepts were quickly excluded and a weighted matrix where each remaining concept was given a grade.

The tests that have been carried out has been meant as a guidance to how UV light is behaving inside a dishwasher and to see what is possible to do and what is not.


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2 The Electrolux company Electrolux is a world leading producer of household appliances. Electrolux is also one of the largest producers in the world of similar equipment for professional users. Electrolux is selling more than 40 million products to customers in 150 countries every year. The company focuses on innovations that are thoughtfully designed, based on extensive consumer insight, to meet the real needs of consumers and professionals. Electrolux products include refrigerators, dishwashers, washing machines, vacuum cleaners and cookers sold under three main brands such as Electrolux, AEG-Electrolux and Zanussi. In some countries there are still local brands such as REX, Marten, Arthur and Husqvarna.

In 2006, Electrolux had sales of SEK 104 billion and 59,500 employees around the world.

Product development and innovation are essential to Electrolux, since 2002 Electrolux has increased its investments in product development from approximately 1 percent of net sales to 1.8 percent in 2006. At the same time, development has become more efficient through global cooperation and coordination of launches between different product categories. In 2006, products that had been launched during the two previous years accounted for more than 40 percent of Electrolux sales.

Consumer insight, understanding the needs of consumers as well as how they think, feel and act when they use household appliances is key essentials to successful product development according to Electrolux. [2]

2.1 Primary Development – prior to product developm ent The workflow within this thesis is supposed to follow Electrolux development process as closely as possible. The product development process throughout the company is called PMF, Product Management Flow and the Primary Development process is a part of it. The Primary Development process consists of 4 different phases with different purposes. The 4 phases have 4 gates with pre-decided deliverables at each checkpoint, as shown below.

Fig.1 Primary development process.


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The purpose of a Primary Development Department is to deal with innovation of products. The two main focuses in dealing with innovation are technology scouting, in order to be able to transfer new solutions developed also in other sectors to the white goods, and consumer focus, to delivery solution and features addressing consumer needs.

Primary development is supposed to identify potential opportunities and reduce the related uncertainties, especially regarding new technologies. Feasibility, time and cost should be verified and proved to be able to hand over the project to product development.

Primary development projects can concern a lot of areas from structure to functionality to features to process and algorithms and they can be large or small, theoretical or concrete, technical or marked orientated. The common factor for all Primary development projects is the high degree of uncertainty.

The output of a Primary development project can be either a proved and well specified improvement of the process or a hardware solution with a tested and evaluated prototype.

A Primary development project is triggered either by consumer needs and a related to new idea or concept which needs to be tested or by technological opportunities that are likely to fit with future the strategic technological view.

Although this department is responsible for exploring future technologies, its activities should be in line with the priorities defined by the strategic market plan.

Depending on the complexity of the project and its level of uncertainty, the duration of the project can vary in time from six months up to one year and a half. The outcome can be uncertain as well thus target are being reviewed at the end of each phase of the project.

It can happen that a project that is dropped and will not continue to product development for different reasons, high cost of the solution, not feasible, not reliable or not relevant, anyhow it is not considered as a failure. The experience gained during the project is valued high, it becomes part of the knowledge of the team and it can be used in the future.

Electrolux has also a specific competence centre with scientists in Solaro, Italy, that is called CTI (Core Technology and Innovation). They support on specific technical issues providing useful theoretical information and experimental support.


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3 Dishwasher technology In order to get an understanding of the dishwashing process, the elements of a traditional dishwasher, are introduced in this section.

3.1 Dishwashers in general The mere cleaning, meaning detaching the soil from the dishware, takes place in the tub. There the upper and the lower basket, which hold the dishes, are situated on slide-in guides. The cutlery is placed separately, either in a small basket that is set into the lower basket, or in a slide-in module which is mostly situated above the upper basket.

Fig.2 Cavity with upper and lower basket

There are different ways to load a dishwasher: most Europeans place glasses and cups in the upper basket, while pots, pans and plates are fit into the lower basket. In some other countries pots, pans and plates are put in the upper basket and glasses and cups in the lower basket. For this reason a maximum flexibility in loading is achieved by making the upper basket adjustable in height.

Upper basket

Lower basket

Tub

Cutlery basket


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Fig.3 Exemplary loading of upper and lower basket

The rotating spray arms detach the soil by a combination of mechanical and chemical effects. The water jets, coming from the nozzles that are part of the spray arms detach the soil mechanically. The water hitting the dishware spreads further and covers all parts of the dishware with the water-detergent solution that dissolves the soil chemically. The rotation of the spray arm is driven by nozzles that are situated at the outer ends of the spray arms. Customary dishwashers have between two and three spray arms, placed under the lower basket and under the upper basket or under the ceiling of the tub.

Fig.4-5 Upper (left) and lower (right) spray arm

Fig.6 Spray arm nozzles

Cleaning nozzles

Driving nozzle


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The filter system is located in the bottom of the tub. It consists of a flat filter and the central filter unit which is shaped as a cylinder and equipped with a handle to make cleaning easier.

Fig.7 Filter system

The filter system also comprises the sump, which is connected to the circulation, the drain pump and the water inlet. The circulation pump provides the water flow for the upper and lower spray arm, whereas the drain pump, which is situated at the lowest point of the sump, disposes the water of to the sewage system. The circulation pump can provide a much higher volume flow (ca. 60 l/min) than the drain pump (ca. 12 l/min) and works much more quiet. The flow heater is placed on the connection line between circulation pump and upper spray arm.

Fig.8 Sump with drain pump, circulation pump and inlet hose

Besides the function of closing the washing chamber also the electronic board of the dishwasher and the control panel are located in the door. Furthermore it comprises the detergent and rinse aid compartments, including the dosing unit for the rinse aid.

Inlet

Drain

sump

Circulation


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Fig.9 Control panel

Fig.10 Detergent and rinse aid compartment

The salt refill and salt dosing unit is located at an easy to reach position in the cavity, it is connected to the water softening unit. The water softening unit can be found under the cavity and gets filled with water through the water filling unit that is located on the side of the cavity.

Fig.11 Salt refill and salt dosing

Detergent compartment

Rinse aid compartment

Dosing unit

Salt refill


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Fig.12 Water filling and water softening unit

Furthermore there are some elements that are not a physical part of a dishwasher but essential for the dishwashing process. Those are the chemicals detergent, rinse aid and water softener, which must be added to yield a proper washing process.

The detergent has several tasks. These are dissolving the connection between soil and dishware, keeping the soil in solution, bleaching the dyestuff and avoiding foaming. Dishwasher salt is used to regenerate the ion exchanger of the water softening unit. The water softener softens the tap water to an acceptable level. The necessary softening action depends on the regional water hardness. If the water is too hard, stains of lime remain on the dishware. Water hardness is measured in German degrees of hardness (dH), where water with hardness up to 10 dH is normally considered as soft. Rinse aid is used to lower the surface tension. Adding the rinse aid, which is done in the last rinse-phase, improves the water run off. Less water on the dishware causes the dishes to dry faster and look more purely.

Detergents off different consistencies are used, like powder-, liquid-, gel- or tablet-formed detergents. As for Europe the most commonly used detergents are the tablets. They consist of pressed powder detergent and are often designed as 3-in-1-tablets, which include a rinse aid and a water softening agent. In this case no supplementary salt and rinse aid is necessary. Tablets are only suited for water with a hardness of 20 dH at most. [3]

3.2 The dishwashing process Since all parts of the dishwasher contribute to a successful dish result, it is important to understand the role every element plays in the process. The dishwashing process is built up of different phases, the pre-wash, the main wash, two or three phases of rinsing and a drying phase. Some of the phases vary with respect to the chosen program in length and temperature. Choosing the quick cycle for example will result in skipping the pre-wash.

The dishwasher is loaded with dishware - china, glassware, cutlery, serving pieces, pots and pans. The correct amount of detergent and, if needed, rinse aid and dishwasher-salt

Filling unit

Water softener unit


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are added. The detergent is filled in for every cycle, but the salt and rinse aid are stored in the dishwasher. They are dosed according to the local water hardness (salt) and the cleaning result (rinse aid).

According to the program the water is heated up to between 40°C and 65°C during the main wash while it is sprayed and sprinkled over the dishware. Running and dripping of from dishware and cavity, the water unites in the bottom of the tub, passes the filter system and is re-circulated by the circulation pump. Between most phases the water and the detached soil are drained by the drain pump and replaced with fresh water. Despite of this, there is always a small system inherent carry-over of water from one phase to the next, approximately half a litre of water sticks to the cavity walls and the dishware plus roughly another half litre that remains in the hydraulic system. Between specific phases a small carry-over of water is desired, for example to take along some detergent.

The functionality of the particular wash phases is explained in the following. In the pre-wash or pre-rinse the soil that is easily detached and food residues are removed with cold water. The main wash, using hot water, should clean the dishware entirely. Sometimes an intermediate rinse is used to clean the fine filter and to renew the water. There can be up to three rinses, one to two cold rinses and one hot rinse in the end. The hot rinse will heat up the dishware, so that the water will evaporate in the drying phase. Some dishwasher models are fitted with a fan that supports the evaporation by an air stream along the water-softening unit, which is filled with cold water. This has a contradictory effect on the drying phase, on the one hand, cooling the air stream will support the condensation of the steam but on the other hand the air is cooler afterwards, so that it can only absorb less water when passing the dishware the next time.

All modern dishwashers today clean the dishes with a very good result. They all use the same technique dissolving soil with a combination of chemical substances from the detergent and mechanical effect from the water from the rotating spray arms. The rotation of the spray arms is generated by the water spraying out of the nozzles on each end of the spray arm. A pump is used to provide water to the spray arms, the effect of the pump is approximately 60 liters per minute. That indicates that the same water is used over and over again to clean the dishes, but it passes through a filter each time it passes the pump. Often there is a turbidity sensor that sense when the water contains particles and soil and is in need of change. The drain pump disposes the dirty water to the sewage system.

A common misunderstanding is that dishwashers are wasting water and electricity. A modern dishwasher uses only about 15 litres of water for a complete program and even less when using the ECO-program. A normal hand wash, when rinsing under pouring water, waste about twice the amount than a dishwasher [4]. A dishwasher consumes about 1.5 kWh which in Sweden costs about 1.50 SEK, so the general opinion that a dishwasher wastes water and electricity might not be correct.


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4 Disinfection methods For all sterilizing methods, cleaning is critical. Biological material may shield the micro-organisms from the source, physical or chemical that is intended to kill them. The regular cleaning before the sterilizing method can also remove a large number of the organisms. A disinfecting feature is not supposed to replace the regular dish program, only to enhance the disinfection. The strong alkali detergent and the rather high temperature of the dishwashers on the market today, provide a 99.9% kill rate of bacteria. [5]

During the pre-study several methods have been studied and a few are presented in this section. The disinfection method selected initially for implementation in this thesis is Ultra Violet Light, and is therefore studied and presented more detailed. The reasons to why UV were chosen as disinfection method is that UV is a well known method for disinfecting and has recently been implemented by one of Electrolux competitors, claiming an increased hygiene. This makes Electrolux curious on how an UV feature for improving the hygiene can be utilized. UV is also one of the methods below that does not include any chemicals and that could function without having to manually do something to obtain the disinfected result.

4.1 UV-C light for disinfection Ultraviolet is one energy region of the electromagnetic spectrum, normally called light, which lies between the x-ray region and the visible region. UV itself lies in the wavelengths of 100 nanometres (nm) to 390 nm and the visible wavelength is from 400 nm to 780 nm.

Fig.13 The spectrum of light.[6]

The optimum wavelength for germicidal action is 264 nm. However, most light sources producing UV-C light transmits the wavelength 254 nm which is very close to optimum for germicidal action as shown in figure below.


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Fig.14 Germicidal effectiveness at a given wavelength [7]

UV-C light works in that way that it penetrates through the cell wall of bacteria and micro organisms and causes a molecular rearrangement of the cells DNA, which prevents it from reproducing. If the cell can’t reproduce, it is considered dead.

Disinfecting abilities

How effective UV-C is against bacteria and viruses depends on the intensity and exposure time. The dosages needed to kill most unwanted bacteria and viruses are normally expressed in microwatt . seconds/cm2. UV radiation is effective against bacteria at dosage levels of 3-30 mJ/cm2 and against viruses at 30-100 mJ/cm2. For detailed information see Appendix 5.

The UV intensity generated from a certain lamp is specified in most cases as microwatts/cm2 at a distance of 1 meter. The intensity at a given distance is proportional to the square of the distance and the time in seconds to reach the germicidal dose could be expressed as:

r

b

I

rdt

2⋅= (1)

bd = Bacteria killing dose (J/m2)

r = distance UV - bacteria (m)

rI = Lamp intensity W/m2

UV-C technology is recognized in the United States by Environmental Protection Agency, EPA, as one of four approved methods for disinfecting water. It is seen as preferable over the other three approved methods, chlorine, iodine, and distillation, because of the cost and effectiveness. More specifically, UV-C works almost instantaneously, leaving no residuals in the water. The technology is fast, does not alter pH, is tasteless and carries no risk of overdose. Further, the use of UV-C is a non-chemical method for microbial control and produces no toxic by-products. World Health Organization, WHO, and Food and Drug Administration, FDA, have approved UV-C as a safe and effective method of water disinfection.


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Liquid disinfection

UV-C is often used to disinfect liquids. In a dishwasher it could be possible to disinfect the flowing water before, during or after the different washing phases. Different liquids have different ability to receive UV treatment due to the absorption coefficient, the same goes for water turbidity. Due to turbidity in the water the disinfecting ability of UV-C will decrease when the number of particles in the water increases.

Table.1 Absorption coefficient, α, of different liquids.

The UV intensity at a specific distance in the liquid is given by the formula[8]: aXeEE ⋅= 0 (2)

0E = Initial Intensity

a = Absorption coefficient

X = Distance

Further calculations can be found in Appendix 4.

Mechanical properties

An interview with a Senior Lecturer at KTH resulted in some facts about the possibilities with using UV-C light. The best material for reflecting UV-C light is aluminium and the best material for transmittance of UV-C is quarts glass as seen in Figure 15.

Fig.15 UV Transmission of different materials. [8]


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The intensity on a surface enlightened with UV-C light, and any other light, decreases with the square of the distance to the source of light[9].

It is possible to use fibre optics to transfer direct light to illuminate all parts of the dishwashers tub. The technique of transferring UV light through fibre optics is used today by dentists for hardening plastic fillings with directly aimed UV light.

Plastic Aging

The biggest issue regarding the use of Ultra Violet light as a disinfecting method is its degrading effect on plastics. Degrading is chemical changes resulting from the materials absorption of light. The chemical changes can be colour changes, bond scission, cross-linking and chemical rearrangements. All organic materials have an ability to photo degrade but this is most relevant for polymers.

Wave lengths in the UV-C region, 280-100nm, have the highest ability of inducing bond scission due to the high rate of energy.[10] The photosensitivity of polypropylene, which is mainly used in the dishwasher, is said to occur primarily at wavelengths below 330 nm.

Fig. 16 Chart relating the energy of radiation at different wavelengths to dissociation energy of different compounds. [10]

Scientists at CTI in Portia have made experiments with UV-C and ABS, PP plastics. They found that after 24-48 hours of exposure the materials had changed colour from white to yellow and after one week the colour had turned brown. They also found that


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the mechanical properties were decreasing. This matter is however investigated further in section 10.1.

The use of mercury lamps

Lamps commonly used to produce UV-C light contain mercury. The mercury use in products is restricted by the Directive on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment[11]. This directive from the European Union is also known as the Restriction of Hazardous Substances Directive or RoHS. The RoHS directive took effect on 1 July 2006, and is mandatory to be enforced and become law in every member state of EU.

The directive restricts the use of six hazardous materials; mercury, lead, cadmium, hexavalent chromium, polybrominated biphenyls and polybrominated diphenyl ether, in the manufacture of different types of electronic and electrical equipment. Though the restricted use of mercury, all UV lamps does not contain mercury and the manufacturers are often approved by RoHS.

Reflection of UV light

To get an effective use of the UV lamp it is important to have a reflecting mirror. The design of the mirror is important to give the optimum distribution of the indirect light from the light source. The shape of the surface will create a different effect if it is parabolic, convex, concave etcetera. The reflecting angle and reflective spread would be affected by the positioning of the lamp, due to shading of its own reflection.

Preferably an aluminium sputtered quartz glass plate should be used as reflecting mirror for UV light. A more economical approach and probably preferred in most cases would be to use a regular aluminium plate. As seen in Table 2.

Table.2 Material reflectance[8]


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4.2 Other methods for disinfection

Ozone Ozone can be used for killing micro-organisms in air and water. Some Municipal drinking water systems use ozone instead of the more commonly used chlorine as disinfecting method. Ozone is a cost-effective method of treating water in terms of that it does not need to be transported or stored as other hazardous chemicals, it can be produced on demand. This can be done in various ways but the must convenient way in this case is by the use of UV light or a corona discharger. Ozone is generated by a wavelength of less than 240nm. For many typical UV lamps a wavelength of 185nm is emitted to create ozone. Wavelengths in this region are also emitted by the sun and have a significant impact for the sustenance of the ozone layer in the stratosphere.

An ozonising device creates free oxide radicals that will react with surrounding O2 and create Ozone, O3, which can react with particles in the surrounding air. For disinfecting purposes the concentration must be between 1-5mg/l.[5] The dose, Time* Concentration, shall by the rule of thumb exceed 5 (min*mg/l). However the Food and Drug Administration (FDA) requires ozone output of indoor medical devices to be no more than 0.05 ppm. But ozone can also be used as a deodorizer. This means that the ozone could be used to remove bad smell, from for example decomposing soil. The ozone has a deodorizing effect from 0.01-0.05ppm which is between the limits from FDA.

How effective the method is depends on three variables:

• Exposure time

• Concentration

• Possibility of the water to dissolve ozone.

The fact that the exposing time is critical to obtain a good disinfection result makes ozonisation impractical for situations involving rapidly moving air or water streams.

For municipal wastewater treatment, the exposing time required to obtain a satisfied grade of disinfection is somewhere around 30 minutes. [12]

In laboratory tests it has been found possibly to reduce the amount of Norwalk virus, Poliovirus1 and Bacteriophage MS2 in drinking water by ozonisation. The virus reductions by ozone were determined using a dose of 0.37mg of ozone/litre at pH 7 and 5°C for up to 5 minutes. The reductions of Norwalk virus were >3 log10 (99.9%) within a contact time of 10 seconds[13], and >4 log10 (99.99%) within 5 minutes. Similar figures were obtained for other viruses and bacteria.

Another way to produce ozone is to use a converter that transforms pure oxygen into ozone, but that equipment is to complex and bulky to implement into a dishwasher.

Ozone could leave an odour and is considered hazardous. This may lead to constructional and functional issues when the air is exhausted from the tub. Another issue with ozone is that it will oxidize metals. This matter has to be investigated further if developing an ozone feature.

Ozone is very unstable and degrades back to oxygen within an hour. [14] More information regarding ozone technology can be found in the ozone chapter 16.


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Heat Heat could be provided in many ways, injecting steam, heating water, heating air, etc. Heated water and heated air are commonly used methods to kill bacteria and microbes. There are a lot of different standard methods to disinfect water, two of them are; to heat water to a temperature of 70˚C for 30 minutes (used for pasteurizing), and the British Standard, DHSS/HTM with a time of 2 minutes and temperature of 82 degrees Celsius[15].

Dry Sterilization Process Dry sterilization process, DSP, is a method used for instance in the beverage industry to sterilize plastic bottles made from PET or HDPE. The method is also used in some applications in the pharmaceutical industry.

Basically the air in the chamber/tub is evacuated to create vacuum by a vacuum pump. Then a solution of hydrogen peroxide is evaporated in the chamber and do immediately condense on the surfaces inside, in this case the dishware, killing all bacteria in a few seconds. Afterwards the condensate is rapidly re-evaporating when the decreasing chamber pressure reaches the condensates vapour pressure and the forming vapour is removed from the chamber by the vacuum pump. This re-evaporation effects a total drying of the bottles and the surfaces inside of the sterilization chamber and completely removes all of the hydrogen peroxide.

Steam Steam is a well known method for cleaning fabrics and disinfecting items not sensitive to high temperatures. The steam has better penetrating ability than boiling water and dissolves stains and soil efficiently. The high temperature softens the grease, oil and fat, but the surface treated must still be wiped or in another way mechanically treated to dislodge the soil.

Pure steam in equilibrium with water-liquid has a temperature of 100°C at standard atmospheric pressure, and occupies about 1600 – 1700 times the volume of liquid water[16]. Steam disinfection is also an effective method for destroying bacteria and micro organisms that are resistant to chemical methods. Steam releases latent heat as soon as it condenses on a cooler object, and consequently produces more rapid heating than boiling water. The killing mechanism of steam is the high temperature, nothing else. The use of steam is preferred due to the excellent transfer abilities that steam can provide, it goes almost everywhere.

All surfaces exposed to steam are at least temporary heated to 100°C, which is enough to kill most of all bacteria and micro organisms. For complete sterilization time of exposure varies with the maximum temperature, different recommendations state 121–132°C for 60 minutes or 134°C for at least 18 minutes.

Other methods used are for low-temperature steam disinfection, which is a process used to disinfect reusable medical devices. The process works by removing air and exposing every surface of the device to saturated steam, below atmospheric pressure, at 73 °C for ten minutes. Sealed, oily or greasy items and those that retain air are not suitable for low-temperature steam disinfection. Another method is the one approved by British Standard Organization, where water is heated to 82˚C for 2 minutes. A third standard method is the one approved by the Swedish Standards Institute, where water is heated to 85˚C for 1 minute. The two last methods should be possible to use for disinfection in a dishwasher.


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Liquid water can not be heated above 100°C during standard pressure. Heating to more than 100°C results in boiling and do not raise the temperature of the liquid water. It is possible though to heat liquid water to a much higher temperature within a sealed container such as an Autoclave or a pressure boiler. An Autoclave is a closed device for steam sterilization that works under high pressure, with super heated steam. When the container is heated the pressure rises according to the ideal gas law, which leads to a higher boiling temperature.

Steam is used to clean a great variety of items, such as: car interior, carpets, sensitive paintings, jewellery, and a lot of other things. In domestic steam cleaning or vapour steam cleaning machines are discharging steam at 115-130°C and are operating at 3 to 4 bar. Commercial machines can have an internal temperature between 182 to 210 °C or even higher. Most devices use dry steam, with an amount of only 5-6 % condensed water, which means that only 5 to 6 % is condensed when leaving the nozzle. It has a direct influence on wetting behaviour and energy content of the steam.[17]

The use of steam in regular dishwashers and washing machines for home appliance has recently been implemented by LG and Maytag in the North American market.

The steam is claimed to enhance the cleaning performance of the machine and is also a strong selling argument that proves that LG is considered as a good innovator.

Potential advantages of using steam in a dishwasher have also been investigated by two expertises at Electrolux CTI department. Their conclusions on the general use of steam were:

• Steam is a good cleaning method, however maybe not for a situation encountered in a standard dishwasher. The steam jet should in that case be positioned very close to and directed at the surface of the dish ware to clean. Unless one is heading for a single item dishwasher and wishes to avoid large redesign work, steam for cleaning is not a feasible feature in a standard dishwasher of today.

• Steam could be used though to soak and dissolve soil, which goes rather good together with the high temperature that the steam provides.

• Steam dissolves the detergent into much smaller particles, making it more efficient against hard stains, grease and soil.

• Steam can be used for drying and as an additional sanitization of dishware. A steam generator of at least 1.5 kW is required to transfer the necessary amount of steam into the cavity at reasonable rate and to avoid excessive losses on the cavity walls. The steam entry may not be localized but has to be evenly distributed or uneven heating of the dishware will occur. High steam pressure is however not required. Thus main efforts using steam should be directed at the last rinse where some energy saving and better disinfection should be possible to achieve.


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5 Different brands and their Hygienic features To get a good understanding of how different competitors and brands are marketing themselves and what they do in the area of hygiene, a market analysis has been performed. The analysis is based on material from the competitors websites, and the numbers should not be taken as facts when reading this report, due to rapid development and updates. The facts have been collected during autumn 2007.

5.1 AEG & Electrolux The two different segments that AEG and Electrolux are supposed to address are not socio-demographically different. The difference between the two segments lies within the personality of the potential buyer. AEG is supposed to address the most demanding customer, who looks for top of the line performance and compares all performance ratios before buying any product. Electrolux is supposed to address customers that are looking for a product with good design, through which they can express their individuality.

AEG & Electrolux Hygienic features

Electrolux today has no special hygienic feature, that’s one reason to why this thesis is investigating the possibilities of implementing one. Electrolux is looking for arguments that appeals to the customer. Adding a feature that enhances the disinfection grade of the dishwasher is addressing both AEG and Electrolux potential buyers. The people looking for extreme performance and the best product on the market will be attracted by a feature like UV-C light and/or steam disinfection. The people that Electrolux is supposed to address are looking for something they can be proud of and put a lot of energy on buying the right product. A special disinfecting feature is something extra that not every dishwasher has and would appeal to those people. The technique used in both brands could be the same but the solution might look totally different depending on the different personalities they are supposed to address. For example could a UV-C light water cleaning device be hidden in an AEG dishwasher and visible fibre optics used in Electrolux to clean the tub and dishes directly.

5.2 Miele The main player in the high end segment is Miele. Miele claims on their website[18] that “Anything else is a compromise” and in the Swedish section “There is no better” (directly translated). Miele has only a small part of the European market, but the brand is very well known and associated to high quality products, thus it is addressing performance demanding customers


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Some of the features that Miele uses to enhance their reputation as one of the performance leading dishwasher supplier are;

• Tilted user interface for ergonomic use

Fig.17 Miele tilted interface

• A great variety of customized programs such as “Pasta/paella”, “Beer glass”, “Plastic” and “No upper basket”. And also the possibility to personally arrange the programs so that you have your favourites first in the menu.

Fig.18 Miele program selection

• Unique solution for cutlery to avoid scratches from each other and fingerprints when picking them up.

Fig.19 Miele patented third cutlery basket

• A program which manages to clean the dishes with a water consumption of only 10 litres.


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Miele Hygienic features

Miele uses a hygiene programme with a temperature of up to 70°C for “total reduction of microbes and bacteria”. In order to market their hygienic program, Miele uses a common method of having a well known external guarantor highlighting the effect of the program and gaining trust among customers. According to Miele website, the German research institute Wfk has confirmed the efficiency of the program and highly recommends it for baby bottles and cutting boards.

5.3 Bosch Bosch is the market leader in dish care in Europe with more than 30% market share. Bosch is a very well known brand associated to high quality and their product range covers all segments, low, middle and high. On the website Bosch has slogans which says, “Perfect technology for a comfortable life”, and “Bosch stand for quality, innovative technology and excellent design”.

Bosch dishwashers have features that are supposed to enhance performance like

• “Vario speed”, a quick program that shortens the dish cycle

• “Aqua vario”, for dynamic water pressure

• “Aqua sensor”, that automatically detects the hardness of the water

• “Delayed start”, programmable starting time

It is easy to find facts about performances of the dishwashers on Bosch website[19], all the figures and numbers of temperatures, time of dish cycles, energy consumption and more. This might appeal to the same segment as AEG, from which customers will look for these facts before he or she buys anything.

Bosch Hygienic features

Considering hygienic features, Bosch is also claiming a hot water rinse with a temperature of 75°C. Neither does Bosch market their hygienic feature in any special way. Bosch and Siemens are having a close partnership and develop and market some products together under the name BoschSiemens.

5.4 Siemens Siemens uses hot water with a temperature of 75°C, plus a drying program called HydroDry, where heated air from the dish cycle is used to kill bacteria. Otherwise the Siemens website provides the same information as Bosch website, meaning no exceptional marketing of hygiene can be found.

5.5 Whirlpool Whirlpool is quite strong in North America, but is also expanding in Europe. Whirlpool is good at communicating the benefits of the products, which are in the medium and low segments.


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GU3600XTS is Whirlpools prestige model. In their product description they are using sentences like: “The formed door styling with concealed electronic controls and a stainless steel tub adds a touch of sophistication to any kitchen.”

Hygienic aspects are not neglected in their marketing. Whirlpool has a function called PowerScour, which are basically 36 spray jets who pre-clean the dirtiest dishes. “All without using a single additional drop of water.” [20]

Fig.20 Whirlpool PowerScour

The Whirlpool model GU2700XTS have a slate interior that reduces visible stains for a premium look. Rack colour also matches the tub colour. Furthermore Whirlpool has an option called Sani Rinse Option certified by NSF, National Sanitization Foundation. This option is a final rinse with raised temperature to 68oC

Whirlpool Hygienic features

Whirlpool does not a big thing about their hygienic feature; they have an additional antibacterial programme phase, which during 10 minutes washes the dish with hot water of at least 68°C.

5.6 Maytag Maytag has recently been bought by the Whirlpool Corporation. They are big in North America where they rely on a 100 year old heritage of quality and performance in home appliances.

Maytag Hygienic features

Maytag is a tough competitor to Electrolux on the North American market and puts a lot of effort in marketing their hygienic steam function. In their introduction movie for their high end dishwasher MDB8951BWW, Maytag[21] shows four slides out of six that relates to the hygiene and two of them to steam. Maytag uses the slogan “The power of steam” and uses just as LG, an external guarantor for their hygienic claims. In this case Maytag claims a killing rate of 99.9% of household bacteria in order to meet NSF (National Sanitation Foundation).


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Fig.21 Maytag steam function

In the users manual there is a dedicated chapter where following are to be read about the “SteamClean option”:

“When selected, this option provides a deep clean and shine by using vaporized water. The SteamClean option will add 24 minutes to your cycle time”. And further on:

“When you choose the SteamClean option, it will add 24 minutes to your cycle. During this time, your dishwasher will generate the steam necessary to deliver a brilliant shine, and better soil and spot removal on glassware.”

The users manual also states that after the “steam” has been injected the dishwasher goes through a final rinse to get rid of all detergent. In that way, the steam will have no effect on water stains left after insufficient drying.

In the picture below the user interface with three optional programs “Steam Clean”, “Hi temp wash” and “Sanitize” can be seen. It is not mentioned on Maytag on the website what the last two options actually do, but they give for sure the consumer an impression of functions related to hygiene.

Fig.22 Three different hygiene programs


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5.7 LG LG is entering the European market with quite an aggressive marketing of white goods, using their well known brand in consumer electronics. LG is really active in the field of innovation and is using industrial design with new innovative technology as a selling argument. In Germany it is possible to buy a LG dishwasher, LD-4224TH, which illuminates the tub for 25 minutes with UV-light after the final rinse to disinfect the tub and the dishware in it. LG has also recently released a model, LDF9810, with steam cleaning on the American market. This together with a rather sophisticated design makes it a serious competitor to Electrolux. The steam cleaning dishwasher is said to “allow for thorough cleaning of baked on foods while using less water than other power scrub methods”. It is also said to “allow for enhanced cleaning performance when cleaning fine china and stemware items on the delicate cycle option”

Fig.23 Steam nozzles

Further LG has a feature called “Dual Intensity™ Wash Cycle”, which enables the user to customize the wash cycle intensity for the upper and lower racks independently. Three levels of intensity (strong, medium, soft) can be customized for the upper and lower racks for each wash cycle. In this way it is possible to, for example, run a cycle with pots and pans in the lower rack on high intensity and delicate stemware in the upper rack on low intensity, simultaneously. [22]

Fig.24 LG design

The picture above shows the “SignaLight™ LED Cycle Indicators”, which are basically four exterior LEDs indicating which wash process is in use. Furthermore the tub is illuminated by two interior LEDs which is supposed according to its feature description clearly show that glasses and dishes have been cleaned.


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Another interesting LG feature for the model LDS5811 is the “Built-in Food Disposer”. The dishwasher has blades of stainless steel to break up food particles which then is flushed down the drain, leaving no baskets to empty.

LG Hygienic features

LG is probably the most active competitor regarding adding features to their dishwashers and hygienic features is no exception. LG also have different models using different hygienic features on different markets today. In Sweden they market a feature called “Turbo dish” which is an extra hot rinse conducted at 80˚C for an improved hygiene. The model called LD-2293THB, on the Swedish market, combines the “Turbo dish” with a “Sterilization function”, consisting of a UV-C lamp that is highlighted for 25 minutes after the final rinse. LG also uses LED tub lights to illuminate the inside of the tub to show that glasses and dishes have been cleaned. In the U.S. LG also has some models using steam to enhance the cleaning performance when cleaning baked on food and to protect fine china and stemware. LG markets the steam feature with the slogan “The gentle power of steam!”


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6 Other products using UV for disinfection An inventory of the market on which kind of products there are today using UV-C light for disinfection shows that UV-C light is used in many applications.

6.1 UV-C light disinfection applications

Flowing medium treatment

UV-C is used to treat pool water, meaning the use of chlorine can be reduced and allows allergic swimmers to enjoy a bath. The cleaning method works in that way that a pump circulates the water through a cross section with UV tubes, killing bacteria.

The same technique as when treating pool water is used for treating drinking water from both surface sources and underground sources. The city of Togliatti has a plant that allows a flow of 405 000 m3/day. The method is very effective and reduces the amount of chemicals needed. UV is also used to treat municipal waste water of large volumes. In Togliatti the municipal waste water has a flow of 290 000 m3/day and is treated with UV.

Fig.25 UV-purifier for pool water, drinking water and treating municipal waste water[23].

The same technique as when treating large volumes is used for home applications. Either the water flows in a coil made of UV-C transparent plastic wrapped around the tube or the UV-C tube is placed in a cross section of the water flow.

Not only flowing water is being treated with UV-C light, also flowing air could be treated using the same technique, in order to get rid of odours and airborne bacteria.

Fig.26 Two devices to clean water in your home and one for mounting inside an air conditioner


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Surfaces treatment

Another area where UV-C light is used to kill bacteria is when disinfecting surfaces of different kind. There are devices for all kinds of applications.

Fig.27 A UV lamp to kill bacteria on big surfaces, and two sizes of handheld surface sterilizers

Food treatment

UV light is commonly used in the food industry to ensure that groceries and vegetables are not infected with any bacteria or virus. Also eggs are treated with UV-C light to ensure that no salmonella bacteria are left on them. The method is to place the items wanted to have treated on a production line and have the line running through a UV cabinet.

Household item treatment

There are some products on the market that that appeal to the really hygiene demanding customers. Often they target what people in general think is a source of bacteria and things that people tend to care extra much for, like your baby’s bottle. Recently LG has released a few models of dishwashers to the market that they claim disinfects the dish by the use of UV-light. In some countries in Asia where the quality of the tap water is not sufficient, there are specific dish sterilizers that uses UV-light to disinfect the dish ware after being cleaned in a regular dishwasher.

Fig.28 Sterilizing toothbrushes, razors, single baby bottles and total dish load


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7 Test of LG UV feature The LG dishwasher with an UV feature, that was recently launched, has been bought and tested considering the functional aspects of their UV feature.

LG has simply implemented an UV lamp in the existing lamp socket by replacing the regular lamp. This means that the dishwasher does not light up when the dishwasher door is open but the solution and the difference is still visible.

The UV lamp is used for 25 minutes after the last warm rinse in the regular cycles or it can be activated on demand by the user by pressing a specific button on the user interface, also in that case it’s the UV light is on for 25 minutes.

Fig.29 LG UV lamp wall mounted between lower and upper basket.

Tests were performed by first stating the intensity of the light at different distances in ideal conditions, which mean a direct hit of the light radiation without obstacles – empty baskets.

In ideal conditions the lamp intensity was calculated to 0.0053W/m2 at 1 meter distance from light source. Knowing the intensity it is possible to calculate the exposure time needed to disinfect a surface at a certain distance from the lamp.

At a distance of 50cm, i.e. the opposite side of the tub, it is possible to disinfect the surface after 78 minutes, considering a killing dose of 10mJ/cm2. This dose eliminates a wide range of bacteria, and is used in all calculations during this thesis to compare different lamp types and concepts. For a complete sterilization this level is to low, approximately 200mJ/cm2 is needed for complete sterilization, see Appendix 5.

The killing dose used in this calculation is clearly lower than the killing dose needed to eliminate various types of germs. Note that the calculation is in ideal conditions were no interferences will occur. In a real life scenario the dishwasher will contain dishware that absorbs and shadows the radiation from the surfaces or items that is intended to be disinfected.

The approach used to measure the light intensity is quite simple: a UV meter has been placed at various places in the dishwasher as shown in the pictures on the next page. The outcomes of those measurements have then been used to estimate the time needed to reach a dose of 10mJ/cm2, as presented in table 3.


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Fig.30 LG Upper basket.

Fig.31 LG Lower basket.

Table.3 Time needed to disinfect

8

9 10

11

12 13 14

1 3

4

5 6

7

2

14

13

12

11

10

9

8

Position Number

1667

36

111

17

1667

52

67

Time to sterilize [min]

8333 7

225 6

538 5

128 4

- 3

333 2

98 1

Time to sterilize [min]

Position Number

Upper Basket

Lower Basket


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As seen in table 3 there is only one position were the intensity is high enough to be disinfected within 25 minutes.

According to the findings and considering the LG application a surface to be disinfected within the 25 minutes claimed for the sanitizing action, has to be placed in a small area at an absolute maximum distance in line with the lamp of 28 cm. The actual usable area for disinfection will be even smaller.

7.1 LG Conclusion The LG UV feature is not efficient in terms of sanitization as they are claiming in the advertisements due to the execution and the type of lamp selected (intensity).

It has to be underlined that it is possible to disinfect dishware and/or tub with UV light, but with a proper intensity, the intensity used by LG is way to low to have an effect within a reasonable timeframe.

In a press release in Sweden, LG has recently changed the claim associating the effect of warm rinse and UV light that “Extra high water temperature (80ºC) and UV-light sterilizing function for better hygienic (dish) result”. This seems to confirm that the introduction of UV light was mainly a marketing feature contributing only partially to the real hygienic result.


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8 Creations of ideas Within this phase a number of ideas are created and developed into concepts. The main focus on the ideas created is the use of UV light. This technique where initially most interesting to Electrolux and has therefore been investigated.

8.1 Opportunities and ideas During the Pre-study a number of ideas and opportunities had already been generated and laid in the background for the Creation of Ideas phase.

The starting points were some facts related to the functionality of the dish washer and the actual washing process:

• In a dish washer cycle water is circulated through the system several times to complete the phase and then drained out and exchanged with new water. .The possibility of reusing the water from some of the phases could be quite relevant since it could allow a reduction of water and energy consumption.

• The water carry over between on cycle and the next is approximately 0.5 litres; this could lead to bacteria growth, generating bad smell if the water residues are left there for a long time.

• If the dishwasher is not opened in a short period after finished cycle, the humid and warm climate inside the tub could stimulate growth of bacteria. A UV lamp could be highlighted every 30 minutes or so after the cycle is finished if the door is not opened.

• The dishwasher filter is usually not cleaned by the user, as recommended in the user manual, this could lead to a collection of soil residuals the in combination with residual water and/or humid environment can promote bacteria growth.

Starting from these facts some consideration and ideas have been developed in the earlier phase:

• Sterilization of the dishware in the tub cavity due to application of optical UV fibres, they can be used to transfer the UV light into the basket, sump or tub without the need and problems with electrical cables.

• Sterilization of the dishware in the tub cavity due to application of germicidal UV lamps and tubes, that are already commonly used, or also with germicidal UV LEDs, but with lower efficiency.

• UV could be used to disinfect water in the washing cycle, inside the machine, not visible to consumer.

• General disinfection by having UV tubes in the tub ceiling radiating the upper basket.

• Specific application with dedicated UV light - for baby bottles, cutting boards, in the upper basket, or for dishwasher filter in the bottom of the tub etc. This can increase the consumer trust in hygienic properties of dishwasher also related to delicate items or items they usually prefers to hand wash reducing the need for hand washing.

.


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• Disinfection in different phases of the wash cycle might appeal more/less to consumers.

The UV light could be used in different to address consumer needs depending on they expectations and in line with the brand promises.

In order to take in consideration also the constrains related to the technology the main issues that need to be taken in consideration have been summarized and shared to have a common understanding

• Ozone: certain types of germicidal UV lamps transform oxygen into ozone. Using ozone is proven to be a very good sterilizing method, but there is a regulation limiting the maximum emission allowed due to its toxicity over certain concentrations.

• Mercury: mercury UV lamps are commonly used in the germicidal industry. Though Mercury is listed in the RoHS directive, thus the application in dishwasher is not allowed unless the lams are easy to remove at the end of the product life to be treated separately.

• Safety risks: short-circuit/tracking between lamp terminals due to water leakage, quartz breakage or gaskets failure with consequences as danger of mercury leakage. This leads to attentive design and a need to carefully define components, rigorous tests.

• Malfunctioning due to soil accumulation on the unit: depending on the application/execution the UV unit may be clogged by particles, minerals and grease etcetera, causing the UV radiation not reaching its supposed destination and lose the disinfection effect.

• Lifetime: UV lamps usually have a lifetime of 5000-10000 hours depending on brand and model. The lifetime is also dependent on how many on/off cycles that are used.

• Aging of plastic materials: plastic materials may absorb UV radiation and cause increased weathering and photo bleaching, leading to a loss or decrease of mechanical properties. Plastics which are strongly affected by UV light are: ABS, PP, PS, PMMA, PC.

• Effect on human being due to misuse: short wave UV radiation (254 nm) is already absorbed in the outer skin, the effects thus being erythema (sunburn) and conjunctivitis (inflammation of the cornea). The possible damage is related to the intensity and exposure time

8.2 Idea creation and concept generation Two separate brainstorming sessions have been performed, the first with members of the Primary Development team the second involving also industrial design.

In the first session brainstorming on UV applications has been executed using the method “As easy as 536” in a group of five persons.

To enhance the idea generation a few trigger questions were given:

• What and how to disinfect? water, sump, dishware, etc…


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• When? Which effect will it have in each cycle?

• Where to place the UV lamp?

• How to reach all areas in the tub?

• Is it necessary to disinfect all areas?

The second brainstorming session was held with the design team from IDC, Italy, at Electrolux. This session was a regular brainstorming split in two parts: the first, as worming up, focused on which items need disinfection; the second on how to use UV light to make a visible feature intuitive and easy to understand for the customers. At the end of this session the ideas were clustered and voted to define which the best were. The outcomes of the first phase, object that can required sterilization, are listed below:

Baby bottles

Toys

Curley straws

Pacifier

Home wine and beer making equipment.

Pharmacy tools

Toothbrush

Cutlery meat knife

Chopping boards

Fake teeth

Braces

Contact lenses holder

Jars for home preservation

Items supposed to be painted

From the ideas created during the brainstorming sessions, a number of different concepts were generated, presented in Appendix 2. These concepts where then evaluated by methods presented in section 8.3 and discussed with Primary Team in order to select which concept should be development further.

8.3 Selection To evaluate the concepts and choose which will be developed further a couple of different evaluating methods were used. These matrixes can be seen in Appendix 3.

As first step an elimination of ideas matrix was built to remove the ideas considered less feasible. The selection has been done considering some basic parameters like efficiency in terms of the ability to address hygienic issues, safety, segment appeal and cost efficiency were evaluated during the selection process. Concepts like UV optical fibre and UV LEDs were removed due to lack of cost efficiency.

Concepts’ screening was based on a method developed by Stuart Pugh called Pugh concept selection.[24] The purpose was to narrow the number of concepts. The advantage of Pugh’s approach to decision making is that subjective opinions about one concept versus another concept can be made more objective. The selection criteria is defined and put in a matrix together with the different concepts presented in Appendix 2.

After narrowing down the concepts a weighted decision matrix was built. The weight factors have been decided by first listing the specific criteria, depending on each concept characteristic. Then the criteria have been compared two by two, deciding which one of the two is the most important. The two criteria compared have to share 1


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point, either one criteria is more important then the other and then receives the scores 1-0, or the criteria are just as important and receives the score 0.5-0.5, no other alternatives are given.

All the scores are written down in a matrix and a weight factor is determined by summarizing all the grades for each concepts, divide that sum by the sum for all of the concepts put together. The maximum value from all concepts is determined and a highest possible grade is also determined. To obtain each concepts weight factor, each quota is divided by the maximum quota and then multiplied with the highest possible grade.

Due to the fact that UV was the main focus in this phase of the project the use of ozone that is tested and presented later, has not been considered in the matrixes.

These matrixes shall not be taken as fact, gut feeling and common sense has to be considered as well. In this phase it was decided to make a visible feature that focuses on dishware disinfection. The concepts are further developed, tested and investigated in section 9.

Selected concepts were visible features that could be easily seen by the user on shop floor and communicate in an efficient way related benefits. They can be summarized in three groups: a door mounted, a ceiling mounted and a sump UV-lamp.

The main factors to be addressed were the emotional perception – as already done by LG moving in this area.

8.4 Patent search A patent search has been performed in order to monitor solutions in use and how competitors are acting on this specific issue. A number of different patents are present within this field since long time, one of the most interesting is US3915180 a patent filed in 1973 on the use of UV irradiation for sterilization in a dishwasher.

This patent state: a dishwasher with energy radiating heat lamps[25] that uses two lamps with UV, infrared and visible light for heating and drying of the dishware. This patent is relevant to this project and also to both LG patents presented on next page. According to the evaluation done in collaboration with Electrolux patent attorney some of LG claims can not be considered novel or involving an inventive step. Due to the time since filing; the use of UV sterilization in a dishwasher seems to be possible without provoking a patent infringement.

Another elapsed patent US3571939 focuses on sterilizing arrangements of dishware: Dish drying and sterilizing arrangement[26], which is using UV light similar to the dish sterilizer.

In LG patent WO2007043795, Washing machine having UV generator[27], claims a dishwasher with a UV lamp or UV LED is mounted in the tub. Another LG patentWO2007021137, Dishwasher with UV sterilization device therein[28], claims a dishwasher with a UV device and a fan to exhaust harmful gas like ozone which could be generated during the sterilization. Both of these patents are protecting solutions that can be relevant in the field of this project and could cause some challenges to the final implementation, anyhow it would be possible to find alternative executions and patent status has to be monitored to verify how they will react and probably change the main claims due to the US3915180 patent .


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9 UV Solution and verification During this phase further investigations, development and tests of the concepts presented earlier have been performed.

9.1 Electrical circuit and component theory A germicidal UV lamp is similar to a regular fluorescent lamp with the difference that the tube contains no fluorescent phosphor; the tube is made of fused quartz rather than being made of ordinary borosilicate glass. This combination allows the 253.7 nm ultraviolet light produced by the mercury arc to pass out of the lamp; in common fluorescent lamps this causes the phosphor to fluoresce, thus producing visible light.

The glowing light is caused by a gas discharge into the fluorescent lamp. The current in the gas discharge causes the resistance to decrease, due to that more electrons and ions flow through a particular area, which bump into more atoms. This releases electrons which create more charged particles therefore the current will climb on its own in the gas discharge, while there is enough voltage. If the current within the fluorescent lamp is not controlled, the electrical components could be damaged.

Unlike incandescent lamps, fluorescent and germicidal lamps always require a ballast to regulate the flow of power through the lamp.

Choosing UV lamp

When choosing the UV lamp for a specific application a number of different aspects have to be taken into consideration.

First and foremost it is important to determine which amount of intensity is needed. A smaller lamp is easier to fit and require a smaller quarts glass window, but will have less intensity which will lead to lower disinfecting ability.

Two types of lamps that are widely used and commercialized by numerous companies as it can be seen in the picture below. Both are quite small lamps but still powerful enough to be used for disinfecting purposes. The tube lamp has a power output of 4Watt with a regular T5 socket and the compact lamp is a PL-S 5Watt with a G23 socket.

Fig.32 TUV 4W (upper) and PL-S 5W


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Both lamps implemented in the final solutions have a UV-C intensity of 9µW/cm2 at the distance of one meter from the lamp. Due to the fact that intensity at a certain distance is regulated by the square of the distance, it is easy to calculate which intensity will be achieved at a certain distance from the lamp. There is also the possibility of having a customized design for the lamp manufacturing it with a specific shape. This could be of use to improve the light spread to a certain area, anyhow this will lead to an increase of cost, and it could be beneficial to some extent. An even smaller lamp could be manufactured with a still usable intensity.

For concept evaluation and lamp selection a number of calculations have been performed. A couple of example calculations are presented in Appendix 4. These calculations have been performed with Microsoft Excel.

Ballast

The ballast mission is to control the current level. In this thesis, two types of ballast have been used. The more basic of the two is the magnetic ballast. This works similar to an inductor which consists of a coil of wire in a circuit that may be bounded around a piece of metal. Electrical current through a wire generates a magnetic field, which with having concentric loops amplifies this field.

When increasing the current in the loop the magnetic field increases. This applies a voltage opposite the current flow in the wire.

A ballast can not stop a change in current, only slow it down. But since the fluorescent lamp is powered by alternating current, it is constantly reversing itself. This means that the ballast only has to restrain increasing current in one direction for a short amount of time.

The second and more modern ballast used is a High Frequency electronic ballast, which can more accurately regulate the current flow through the electrical circuit. In comparison to the magnetic ballast it uses higher cycle rates; they do not generate a flicker or humming noise coming from the ballast, which can be generated from the magnetic one. Different lamps require specific ballasts designed to maintain the specific voltage and current levels needed for various lamp designs.

Starter

A fluorescent tube that is using magnetic ballast needs a starter to help the lamp light. The most commonly used starter is a glow tube starter which is a small tube filled with gas. When the voltage is sent to the lamp, the applied current causes the starter contacts to heat up and open and as a result the flow of current is interrupted, whereas the glow tube lights. When the fluorescent lamp is turned on the starter is a closed switch. The filaments at the ends of the glow tube are heated by electricity, and they create a cloud of electrons inside the glow tube, which heats a bimetal contact. The fluorescent starter is a time delay switch that opens after a second or two. The inductive kick generated at the instant of opening, triggers the main discharge in the fluorescent tube and lights the lamp.


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Circuit

The circuit design is affected by the type of lamp to be used and consequently by the different ballast. If using magnetic ballast (B), a capacitor (C) of 2pF is needed, and when using a tube, a starter (v) is needed, as it can be seen in Figure 33-34. These components have to be compatible with the preferred lamp. [8]

Fig.33-34 A magnetic ballast circuit with tube respectively compact lamp.

If using high frequency ballasts no starter or capacitor is needed. As seen in Figure 35-36.

Fig.35 High frequency ballast circuit with tube lamp

Fig.36 High frequency ballast circuit with compact lamp


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10 Tests of UV abilities There are several ways to test the concepts regarding functionality and effect. Disinfection efficiency and material properties have been the main focus for the use of UV. Mock-ups were built to test the concepts considering lamp placements, dishware disinfection abilities and lamp feasibilities.

10.1 Disinfection tests A methodology to evaluate disinfection efficiency has been defined in order to compare the different executions. An intensity meter calibrated for the wavelength 253.7 nm has been used to evaluate the potential in disinfecting surfaces and dishware. The sensor was positioned in various places within the dishwasher measuring the light intensity and then calculating disinfection time.

First of all it is important to state which organisms shall be eliminated. Different bacteria need a different killing dose; thus defining bacteria targeted defines the elimination dose needed.

For all measurements and doses presented in this report a killing dose of 100 J/m2 or 10mJ/cm2 is calculated since a wide range of bacteria is eliminated by this dose, see Appendix 5 For many bacteria this level is too low and therefore the dose needed for disinfection should be even higher.

Fig.37 UV Intensity meter calibrated for 253.7 nanometre, displayed in µW/cm2.

The evaluation of the UV treatment method and/or lamp position was performed considering three aspects:

• Time needed to disinfect

• Treated area

• Power of dose

There are some issues that need to be taken in consideration while performing measurements with UV meter in order to ensure reliable results. The sensor in the UV meter may be in shadow from light directed from the side. This could cause incorrect values.


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Tests of an empty dishwasher

Tests were performed during ideal conditions: considering a direct hit of the UV light everywhere inside an empty dishwasher. The tests indicate that for a direct hit, 4 minutes of UV treatment are needed to disinfect an area 50cm far from the source. This can raise the issue of plastic aging if every part within the dishwasher shall be disinfected in ideal conditions.

Tests of a fully loaded dishwasher

When dishware is loaded into the dishwasher, the results from the intensity values are significantly reduced. The dishware absorbs and/or reflects light and shades the surroundings, with the consequences of greatly reducing the disinfecting effect of the dishware in total. Between glass and porcelain there will be shadowed parts that the directed UV light will not reach. Therefore it is more efficient to direct the light to the dishware that needs to be disinfected addressing specific areas.

Considering for example the concept with a UV lamp for the sump, the light should be focused on the sump and filter area and eventually invest the bottom of the tub. The dishware in the lower basket will anyhow be disinfected but only in the bottom edge.

For the concept with an UV lamp mounted in the door, the cutlery basket will receive a great amount of UV exposure. Approximately 20-60s is needed for disinfection of cutlery. This positioning of the lamp will also affect the surfaces that are exposed in both upper and lower basket and are therefore feasible areas to focus the light on.

Tests of upper cutlery basket

Additional verifications have been done considering a dedicated application for the upper basket The upper spray arm was replaced by a germicidal PL-S lamp of 5 Watts. The existing knife rack was placed underneath the lamp. Either this existing tray or the upper cutlery basket could be used as a dedicated disinfection zone.

The UV meter was positioned at a number of different places in the knife rack. The tests gave an area of about 32x32 cm that could be disinfected within 4 minutes. If a disinfecting time of less than 1 minutes is needed an area of approximately 20x32 cm could be used. As seen in Figure 38.

Fig.38 Treatable area with central mounted ceiling UV lamp.


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Test conclusion

The best way to use a UV lamp as a disinfecting feature is to direct the light to a specific zone.

Disinfection between plates is impossible within a reasonable time due to reflection/absorption and shadows between them.

Disinfection of an empty tub is possible to, but could raise issues of plastic aging, and it seems anyhow not to be so relevant for the consumer.

Sump disinfection does not reach any other areas than the sump and disinfection of a quantity of bacteria in the soil is pointless due to the fact that only the outer layer of bacteria is eliminated. Thus it exist living bacteria beneath the first layer.

10.2 Visual tests When focusing on a specific area as the cutlery tray it is a problem to verify that the light hits every spot on the cutlery. Therefore a dedicated method had been developed to evaluate the efficiency of the application; a fluorescent dye was painted on the cutlery in order to highlight if the shaded areas were hit directly and/or by reflected irradiation. These tests were performed ocular with the use of a black light. Black light comes from a black painted UV lamp with a wavelength of 370 nm used to highlight fluorescent materials. As seen in Figure 39-40.

Fig.39-40 The painted spots on the cutlery fluoresce by the black light.

These visual tests showed that although large amounts of the cutlery surfaces were hit by the radiation not 100% of them was disinfected.

The UV radiation is not reaching all of the shaded parts of the cutlery neither directly, as could have been expected, nor due to reflection; a maximum efficiency of approximately 50% can be anyhow guaranteed


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10.3 Investigation of effects of UV on plastic mate rial One key issue to be verified is how different materials are reacting to UV, to be sure that nothing of what the consumer would introduce into the DW could be damage by UV radiation, or if it can be to give the advice in the user manual. As mentioned before the main problems can occur with plastic items and plastic components inside the tub.

Some dedicated tests were performed to investigate if materials in the dishwasher could withstand UV light.

Two sets of tests were performed the first using a 4Watt UV tube lamp and polypropylene plastic parts. Lamp has been positioned at a distance of 20cm from the plastic part and the second with a 5 Watt compact UV lamp, PL-S, at a distance of 2cm from polypropylene parts.

Two identical polypropylene parts from a dishwasher, where one was exposed to the UV radiation 250 hours and periodically checked to verify changes in colour or mechanical properties between the two.

When and if decolourization occurs, it is possible to calculate the maximum achievable dose per dish cycle during a lifetime of the dishwasher. Considering that the dishwasher is expected to run every day for 10 years, meaning 3650 cycles during its lifetime, plastic components should withstands that lifetime also considering the exposure to UV light

Plastic aging results

Tests with a 4 Watt UV tube at a distance of 20cm from Polypropylene parts showed that after 250 hours no indications of material changes had occurred.

Tests with a 5 Watt compact UV lamp, PL-S, at a distance of 2cm from Polypropylene parts showed that after 250 hours the first indications of colour changes occurred. This together with the estimated cycles give an approximation of the maximum dose possible if there is no change of the polypropylene material.

min42463650

60250 2

≈=⋅s (3)

This means that for every cycle the lamp could be used for a maximum of about 4 minutes for a scenario with Polypropylene parts 2cm from the UV lamp. Depending on distance to the treated area, the time needed for disinfection could be even lower. If the distance to plastic parts is further the exposure time could be even longer.


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11 Concepts During the solution and verification phase the different UV concepts selected earlier were sketched in CATIA v5. These sketches were created to get a feeling of the sizes and possibilities with different lamps and armature. Mock-ups were built to get a feeling of how big the impact of different lamps mounted in different places will have on the tub, user experience and disinfection ability.

11.1 Lamp armatures The main focus is where the lamp shall be placed inside the dishwasher; this is important for a number of reasons.

• Efficiency: the disinfection performance is proportional with distance and angle of attack of the UV lamp.

• Visibility of the solution: the lamp position is also important to get the attention from the consumer. A visible and intuitive lamp position is a great selling point and holds an opportunity for the brand language and the storytelling of the product.

Some execution can be seen in the pictures below, Figure 41- 43.

Fig.41-43 Different approaches to a door/wall mounted UV tube

To direct the light to a specific area in the upper or lower basket it is preferable to have the window inclined in the right direction, in that case additional extra space for the UV


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lamp can be required as it can be seen in Figure 41, on the left side. These sketches have used the 4W UV tube presented earlier. One important aspect to be considered is to get the window as small as possible due to the required use of expensive quarts glass. Another issue that could lead to problems, is on how to assembly it inside the dishwasher. The device should preferably be mounted in one piece to simplify the process. Therefore the solutions must be wisely considered.

Fig.44 Ceiling mounted UV lamp, sketch by IDC

Some sketches of concepts were gathered from the design team in Portia. Figure 44 indicates how a final solution may look.

11.2 Flip down item holder To have a dedicated zone an application on a special holder for the items needing disinfection has been already mentioned before. The example below has been considered as reference, Figure 45.

Fig.45 Item holder - UV zone

The solutions of the armature of the lamp may be combined with this item holder positioned in the upper basket, in order to create the feature and implement it in the dishwasher.


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12 Hardware and Solutions During development and testing it was clearly found that two main zones could be used to achieve positive disinfection. Those were: the upper cutlery/knife rack zone and the cutlery basket zone. Therefore the ceiling mounted and the door mounted UV lamp concepts were most feasible for prototyping.

During this phase the final solution where created, implemented and tested in the DW.

12.1 Solution design The subject of a primary project is, as described earlier, to verify feasibility of different solutions solving the main uncertainties, before transferring solutions or features to product development. Manufacturability, material selection, electrical set up and other related issues should be taken in consideration along the project development in order to delivery solutions that are feasible for industrialization, but not all these aspects have been deeply taken in consideration in the current study.

In particular have a couple of important constraints been taken in consideration while developing the features been taken under consideration:

• The lamp should be easily assembled and disassembled, preferably in one piece for the specified zone/application.

• The quarts glass window size has to be minimized, due to cost issues.

• To guarantee disinfection efficiency some minimum requirements should be met and combine with constrains on lamp size – thus 5W PL-S lamp is considered for the door mounted feature and a 4W tube lamp is considered for the ceiling mounted feature,.

• Electric wiring needed has to be considered.

For both solutions the High Frequency ballast is used and connected directly to 220V 50Hz. In a final implementation the control of the lamp and ballast has to be controlled by the DW processor and presented with a user interface, which is discussed in section 12.3.

12.2 Prototypes The prototype were developed with CATIA v5 and manufactured with a SLS machine. The have been developed and tested without a quarts glass window due to the availability and cost of material, timing to get the part done.

This cost will decrease if mass produced. However since it is possible to evaluate the solution also without the quartz window at this phase of the project was not mandatory to have the samples.

First concept: door mounted UV lamp for cutlery bas ket

To make an intuitive and visible UV feature, that still has a certain degree of accuracy of the disinfection, this concept is focused on the cutlery tray in the lower basket.

The lamp is then assembled on the door at the same height of the detergent dispenser, as it can be seen in Figure 48. The lamp socket is separated in two plastic parts, one


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containing the lamp armature (Middle Figure 48) and one with the mounting bosses (Left Figure 48). The first part can slide into the outer visible part which can be mounted from the front of the DW door.

Fig.46-47 Catia sketch of the two parts, partly slide in.

Considering the prototype (Fig 48) it can be assembled with a similar approach to as the one used to assembly the detergent dispenser. The visible part has boss holes with ribs to mount the part on the door plate. Furthermore there is a profile to fit a gasket in order to prevent water leakage from the armature.

Fig.48 Lamp in door parts from SLS

Fig.49 Lamp mounted inside the dishwasher

When the lamp is mounted in the door the feature is very intuitive and visible to the consumer. When the consumer opens the dishwasher in the shop floor he or she will see something totally different compared to the competitors. This could increase the perceived value of the product and increase the brand equity.


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Second concept: ceiling mounted UV tube

This concept is made to focus on the upper cutlery basket, knife rack or an area with similar appearance. The variety of items that could be placed there for disinfection is quite big. The most suitable solution in terms of UV lamp is in this case a tube lamp due to the lack of space in the tub ceiling; the execution of the lamp holder can be seen in Figure 50.

Fig.50 Ceiling mounted tube SLS assembled

This concept is using the same assembly principle as the ceiling spray arm. The same mounting hole is used and a similar twist snap fit, as seen in Figure 51. This makes an implementation in the existing product line easier, since no changes in the tub are needed.

Fig.51 The use of the upper spray arm fit makes the feature easy to implement in an existing product line.


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Fig.52-53 Ceiling mounted tube parts, SLS (left) and Catia (right).

Fig.54 Ceiling mounted tube in dishwasher.

This feature does not really allow an optimum use the ceiling space, and the light spread is not optimized as well due to the too narrow space between the lamp and the tray it self. A new prototype could be made to follow up the solution in which the UV light should be mounted closer to the ceiling.

The tests presented in section 10.1, showed that an area of about 32x32 cm that could be disinfected within 4 minutes. If a disinfecting time of less than 1 minutes is needed an area of approximately 20x32 cm could be used. This indicates how the dimensions of the cutlery tray are limited in the horizontal direction.

Another approach could be to have the whole visible lamp armature made of quarts glass and therefore increase the UV spread, but that seems not to be feasible in terms of costs.

12.3 Feature visualization There are several ways to communicate the use of the product and visualize new features. One way is to have something clearly visible and differentiated inside the dishwasher - highlighting specific zones and ways to arrange items that needs


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disinfection. Another way is to communicate from the user interface in order to capture the attention and raise curiosity.

Considering this second approach there are different options to execute it, playing with the LCD, with the buttons.

Considering the LCD a black light in the front could light up “invisible” text on the DW front, communicating that the UV feature is being used.

This feature can be part of a specific program, implemented in existing programs or be manually activated when needed. Buttons on the dishwasher could be designated to be used for the UV feature, as seen below.

Fig.55-57 Examples of how to highlight the UV feature

12.4 UV Conclusions Considering UV light application, the most important issue is the fact that only a direct hit of the UV irradiation will eliminate bacteria on a surface. This fact will significantly reduce the efficiency of the application when considering the use for surface disinfection; only one side of cutlery or dishware could be disinfected without the use of several lamps.

Furthermore the delivered efficiency depends also from selection of the proper intensity for the UV lamp and not able to provide 100% disinfection, but it’s also not totally useless, depending on how the application is executed.

However, UV light could be used for other purposes, as preferably to treat water, either for reuse or within existing dish cycle. These matters will be discussed later in the ozone section.


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13 Ozone in a dishwasher During the development of the UV feature it was found clear that UV will not have a real impact on the hygienic results unless having really complex solutions. Therefore it has been decided to include in the content of the thesis a dedicated session to an alternative technology: the use of ozone in a dishwasher. Several possibilities can be seen, but will need further investigation to draft the final conclusions.

Consumers have put it forward that bad smell from decomposing soil or unclean dishware is one of the biggest issues with dishwashers. Ozone may be used to deodorize air with concentrations not exceeding the hazardous limits. To be able to disinfect bacteria in air the ozone level has to be higher than the limits and could therefore be very difficult to obtain in a safe way inside the dishwasher.

13.1 Ozoniser for odour removal A simple prototype was built, by implementing an ozoniser in the dishwasher’s ventilation chamber. The ozoniser was switched on for about 1-2 seconds while the fan re-circulated the air within the dishwasher. This could be an option to turn on when the dishwasher has been left closed and unattended for a particular time period to prevent bad smell from unwashed dishware or decomposing soil.

Fig.58 Ozoniser mounted in ventilation chamber.

The ozoniser application has constrains to be considered: first of all it does not work in of in humid and wet conditions; the ozoniser cannot be in contact with water which could damage the ceramic plate.

This open a question on the application defined, since condensation will occur within the existing ventilation chamber. If condensed water comes in contact with the ceramic plate while running, the device could short circuit.

Another issue is that due to the surrounding humid environment the ozone production will decrease. In a humidity of 70-90% the ozone production will decrease by 90% compared to when the air is dry. If the humidity of the air is above 90%, the ozone output will decrease rapidly. [29] To get a more effective ozone production in a humid


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environment, a desiccant could be applied at the input hole of the air flow or a bigger ozone generator could be used.

Though the humidity level is important for the ozone output, this might not be of any concern in this case due to the way the ozoniser should be used. The ozoniser shall be used to deodorize and neutralize the air in the tub cavity from bad smells. The smell is not an issue immediately after a dish cycle has run when the air humidity is high. Bad smell takes several hours to occur due to decomposing of left over soil on dishware or sump filters. Therefore the use of the ozoniser could be postponed and started after that the door has been closed without a performance of a dish cycle for a number of hours. It can be assumed that the delay between the washing cycle and the use of the ozoniser will make the left over water dry and humidity to decrease, making it no problem to the ozoniser.

Ozone deodorizing tests

Ozone has been used as deodorizer. To evaluate the efficiency a test panel has been run in order to get a feedback from different people on the perceived odour level before and after the use of odour removal device.

When tests with ozone are performed, it is important to never exceed the limits of concentration in the air allows from the standard, see section 4.2. Though ozone is used to remove odour, it creates odour itself into large quantities. It deodorizes the bad odour with a sharp smell, which by many can be considered a bad odour itself.

To test the deodorizing effect, a compound of decomposing egg and minced meat were mixed.

• This compound were placed in the dishwasher and smelled by a test panel of 5 persons.

• After the “bad smell test” the ozoniser was turned on for 2 seconds followed by an air recirculation from the built in fan.

• Followed by the test person smelled the dishwasher inside again.

Deodorizing conclusions

To deodorize air from bad smell, ozone could be used to some extent. When the air is deeply contaminated by bad smell the ozone will affect the air in a positive way. But when there is only a small portion or no bad smell the ozone might have a negative impact.

The perceived bad smell is very personal and therefore an ozone feature alone could be a negative or positive feature depending on users personal perception.


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13.2 Ozone in water One possible way to use the ozone potential is to treat water. When ozone is oxidised in water the amounts released to the air is much smaller, due to the ability of ozone to dissolve in water. It is therefore easier to prevent leakage of ozone to the surroundings. Ozone is highly instable in water and decomposes to oxygen within a very short time. In pure water, less than half of ozone activity remains after 20 minutes. In more turbid water the time is even less.

A couple of indications from the use of ozone in other businesses have given a couple of possible opportunities.

• It may be possible to reuse water from the last rinse and for pre-wash in the next dish cycle, saving a consistent amount of water. To guarantee a hygienic pre-wash the saved water has to be disinfected to prevent bacteria and algae growth. This can be done by using either UV or Ozone.

• Treat water in dish cycle to increase the hygienic performance, and possible lower the temperature needed to create a hygienic result.

• Ozone can be used to dissolve detergent to make it more efficient, which could lead to less use of detergent

To perform test on these theories, a couple of prototypes where built.

Saved water treatment Considering the use of ozone to save water from last rinse, two main approaches have been considered. Either treat water before it enters a water tank or treat the water within the tank, as seen in figure 59.

Fig.59 Two approaches for treating water from last rinse.

To treat water, a standard ozoniser with a built in air pump from TrumpXP has been tested. The air pump power in combination with bad design of ozone housing is

1. Last rinse

2a.Disinfection

3a.Water tank 4a.Pre wash

2b. Continueos disinfection

2b. Water tank

3b. Pre wash


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reducing the effect of the device, which was therefore rebuilt to be able to treat the water. See Figure 60.

Fig.60 Ozoniser from TrumpXP with built in air pump to ozonise water.

To save water, a tank is needed; this tank should contain 3-4 litres to be able to save all the water from the last rinse. The disinfection treatment should be directed either to the inlet water or within the tank as described earlier.

Fig.61 Water tank with ozone disinfection.

To achieve an ozonising effect within the tank, a similar technique to aquariums, using an air stone could be used. An air stone reduces the size of the air or ozone bubbles in the water and therefore increases the ozonising performance.

To treat water in a closed area like a water tank or a closed circuit is easier, considering to not exceeding the restricted ozone levels in the surroundings.

Treat water within dish cycle To treat the water within the dish cycle, one feasible and rather simple way is to attach an air pump to the ozoniser and pump the ozone into the water. Another commonly used technique to ozonise water within a water flow is by using a venturi injection disperser unit.

The ozonising could also be done directly to the sump to both treat the filter area and the flowing water.


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Fig.62 Example of inlet valve for sump treatment.

By using ozone in water it may be possible to reduce the amount of chlorine in the detergent. Ozone has similar and sometimes better bacteria killing abilities and leaves no residuals in the waste water. Contact time for antimicrobial action is typical 4 to 5 times less than those for chlorine.

As presented in section 5.2 the reductions of Norwalk virus were 99.9% within a contact time of 10 seconds, and 99.99% within 5 minutes. This may give an indication of the abilities. A dishwasher is stated to be disinfecting the dishware to 99.9%.

On the other hand cannot ozone be used in water temperatures over 40 degrees Celsius. This rapidly increases the reaction rate back to oxygen.

Section disclosed due to confidentiality.

13.3 Ozone leakage One big issue when using ozone is the leakage. Ozone is hazardous and has to be closed inside the DW until it has reacted back to oxygen or been broken down on its way out of the machine. This has to some extent been done by using a carbon filter during tests. A similar approach with using carbon filters may work but need further investigation and development to be truly functional.

Another way to remove ozone from the air or water is to either race the water temperature higher levels or introduce humid air. These techniques are off course easy to implement in a dishwasher.


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14 Discussion and conclusions The activity done has followed the process defined in Primary Development. A primary development project at Electrolux is supposed to reduce uncertainties regarding new technology, feasibility, time and cost before handing the project over to product development. This was the case in this project where it was found clear that dishwashers are disinfecting the dishware to 99.9% and that UV does not give a substantial benefit to the hygienic result in this specific application.

The focus on a visible UV solution disinfecting the dishware in the cavity, that was the main task of the activity, has been proved not to be relevant from a technical point of view also if it could have an impact on consumer emotional perception.

Still UV technology can be use for other applications inside the dishwasher with really promising benefits –like the reuse of water. Furthermore another technology has been considered in the last phase of the thesis in order to create and provide to the primary team additional inputs for further development. The focus in this case has been the use of ozone in dishwasher application. It seems there are good potentials especially related to the water reuse that can be really interesting, especially in a context in which environmental concern is becoming more relevant every day.

14.1 UV feature As mentioned above the use of UV in a dishwasher will most likely not affect the hygienic result, therefore an implementation of a UV would be a marketing feature more than something that improves the hygienic result.

The prototypes developed have the ability to claim a certain degree of disinfection. But, the items placed in the disinfection areas have to be placed in away that achieves a direct hit from the UV irradiation. Due to the uncertain direction of UV irradiation, an even disinfection level of the dishware will be hard to achieve. It is practically impossible to aim to disinfect a larger area of tub and dishware.

Considering lamp power the prototype lamps have a good ability to achieve surface disinfection in ideal conditions. They could have a smaller size, thus decreasing the needed size of the quarts glass window.

Branding Though LG is claiming to achieve a degree of disinfection with their UV lamp, which tests showed is impossible, a to some part functional UV disinfecting feature is possible to create. If the claim of functionality is not exaggerated and the UV output is high enough, the feature could be a trustworthy solution with high tech appearance that adds emotional value to the product. The storytelling of the Electrolux brand as an innovative, reliable, high end brand could be enhanced by a feature like this.

Due to the fact that the technique and appearance of a dishwasher is very similar between brands and that the market is fairly saturated, the brand language has to play a big role. To create the brand language you have to, in some cases take a chance to provoke the consumers mind. To give them something to talk about and think of, when they see the Electrolux or AEG brand.


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Diverse markets Furthermore different markets have different approach to technologies for disinfection. In a market were disinfection is important due to different aspects as bird flu, bad water quality or other issues, an UV feature like this might be suitable. In a perspective were it is not really sure that the dishwasher deliver 99.9% disinfection of the dishware, a feature to enhance that feeling could be really useful.

In some markets the term Ultra Violet Light may have a bad reputation due to the fact that UV light may cause cancer. In the markets where this might be an issue, the advantages and the safety of the product has to be declared.

14.2 Ozone concepts The use of Ozone to remove bad smell is not recommended due to the creation of the sharp ozone smell.

Ozone has a great ability to disinfect surfaces and water, and opens up a lot of different possibilities for use in a dishwasher. As indicated there are a few indications of abilities of ozone that has to be investigated further, preferable with CTI before making a final conclusion:

• Dissolve detergent – reduce detergent use

• Disinfect water – Treat water during cycle

• Disinfect last rinse water - To reuse water

However, one big issue is how to keep the ozone within the dishwasher and not cause leakage of ozone, due to the fact that ozone is toxic and hazardous to humans in too big quantities. This leakage has to some extent been closed in a tank by using a carbon filter during tests, but need further investigation and development to be truly functional.

Regarding water savings, seen in a wider scope, if every Electrolux dishwasher could save 4 litres of water by reusing it from the last cycle. A very harsh approximation could give a total water saving of about 4-5 billion litres of water annually by the machines sold that year globally (3.3 million DW sold in 2005). If continuing with estimations, this water is enough to feed drinking water to 13.2 million people annually.

Further discussions and conclusions disclosed due to confidentiality.

14.3 Process The Primary development process is similar to other stage gate models, with clear deliverables at each gate. Within this project iterative project development has been practised. When more information had been collected of the uncertainties of the UV technology this iterative development where very useful. When in the phase of hardware and solutions for the UV feature, it was decided to within the time limit repeat the concept development phase with focus on ozone instead.


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References [1] Krische, B (2005). UV-disinfection, Electrolux internal report.

[2] AB Electrolux, (2006). Annual report.

[3] Krische, B (2006). Water softening in small dishwash applications, Electrolux internal report.

[4] Stamminger, R.(2004) Geschirrspülen in Europa. ernährung im fokus. Juni 2004. p.154-158.

[5] Krische, B., Spizzo, F. Hygiene improvement, Mapping of antimicrobial measures, Electrolux internal report.

[6] The Science of UV Light, Emperor Aquatics inc. http://www.uvcomparison.com/uvscience.php

[7]UVC Production by Germicidal UV Lamps, American Air & Water Inc. http://www.americanairandwater.com/lamps.htm 2007-09-21

[8] Philips Electronics, (2006).Ultraviolet purification application information -Perfection preserved by the purest of light. Philips Technical Report.

[9] Benson,H. (1995) University Physics, John Wiley & Sons, Hoboken.

[10] Feller, R L. (1994) Accelerated Aging: Photochemical and Thermal aspects. The J.Paul Getty Trust.

[11] Directive 2002/95/EC of the european parliament and of the council of 27 January 2003 on the restriction of the use of certain hazardous substances in electrical and electronic equipment.

[12] Solomon, C et al. (1998) Ozone Disinfection. The National Small Flows Clearinghouse, www.nesc.wvu.edu/nsfc/pdf/eti/Ozone_Dis_tech.pdf

[13] Shin, G-A., Sobsey, M D. (2003)Reduction of Norwalk Virus, Poliovirus 1, and Bacteriophage MS2 by Ozone Disinfection of Water, Applied and Environmental Microbiology, July 2003, p. 3975-3978, Vol. 69, No. 7 0099-2240/03

[14]Ozone Production and Destruction, Goddard DAAC, http://jcbmac.chem.brown.edu/myl/ct7/ozone/ozone_cycle.html, 2007-12-18

[15]Evaluation of cleaning and disinfection processes perfrormed by automatic washer/disinfectors, Do Carmo, M. http://www.infectioncontroltoday.com/articles/551inside.html, 2007-10-30

[16] Steam characteristics, http://www.thermexcel.com/english/tables/vap_eau.htm, 2007-10-21

[17] Krische, B et al(2007). Steam Cleaning in Dishwasher, Electrolux internal report.

[18] Miele hompepage, www.miele.com, 2007-12-18

[19] Bosch hompepage, www.bosch.com, 2007-11-28

[20] Whirlpool hompepage, www.whirlpool.com, 2007-11-28

[21] Maytag hompepage, www.maytag.com, 2007-11-28

[22] LG hompepage, www.lge.com, 2007-11-28

[23] Volkov, S et al. Ultraviolet radiation - state-of-the-art method of water disinfection


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[24] Ulrich K T., Eppinger S D. (2003) Product Design and Development. McGraw-Hill companies inc. New York.

[25] Dishwasher with energy radiating heat lamps, (1975) US3915180, GEN MOTORS CORP.

[26] Dish drying and sterilizing arrangement, (1971) US3571939, Beverly Paul.

[27] Washing machine having UV generator, (2006) WO2007043795, Shin Dong Hoon et al.

[28] Dish washer with UV sterilization device therein, (2007) WO2007021137, LG ELECTRONICS INC

[29] TrumpXP Electronic customer care.


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Appendix 1 – Risk analysis A Failure Mode and Effects Analysis (FMEA) were performed to analyze potential risks within the project. A FMEA classifies the potential risks by severity or determination of the failure's effect upon the project. The model is widely used in the manufacturing industries in various phases of the product life cycle. Failure causes are any errors or defects in the process, design, or product. In this case the FMEA is focusing on the thesis project. Effects analysis refers to studying the consequences of those failures.


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Appendix 2 - Concepts 1. UV lamp wall mounted in existing lamp socket.

The lamp uses the same connection as the existing lamp. This means that no redesign of the tub is needed.

Advantages

• Combine both visible and UV light. • Selected area – Right side of baskets

becomes radiated. • No redesign of tub needed. • Possible to place lamp beneath or

above upper/lower basket. • Possible to combine 2-3 lamps to

radiate at a selected area. • Appeal to AoS and SE.

Disadvantages • Only suitable in one side of tub. • Will only radiate one side of

dishware and only the first (closest) object.

Open Issues • May collide with basket. • LG uses similar technique.

2. Door mounted UV lamp

The UV lamp is placed in the door and consists of an aluminium reflector, quartz glass window.

Advantages • Stylish design - appealing to AoS. • Very visible feature - appealing to

AoS. • Positioned in height between the

baskets, it will reach most areas. • Focus on cutlery basket possible. • Spacious for connections, lamp

etcetera in door.

Disadvantages • The radiation spread will be in the

front part of DW. • Appearance more important than

functionality • Redesign of door needed

Constrains to be considered: • 90 degrees spread could be suitable for cutlery basket and upper basket. • Aligned on the door with Detergent dispenser

3ab-4ab. Water flow treatment

In this concept UV is used to treat the flowing water during wash cycle. The water will always be disinfected and therefore enhance the hygienic result. An UV lamp is placed either in the water flow or with a UV transmitting coil around a lamp. The coil is made of UV-C transmitting plastic, preferably FEP, with a surrounding aluminium reflector. An approximation of the effect is to place a 5W lamp less than 3cm between source/bacteria with a water tube of length 15cm and diameter 2cm. Then it is enough to disinfect a flow of 30l/min with 100J/m2.

3a. Within existing hydraulic system. UV lamp with spiral water tube. 3b. Within existing hydraulic system. Lamp inside water flow. 4a. Bypass water in regular flow. Lamp inside water flow. 4b. Bypass water in regular flow. UV lamp with spiral water tube.


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Advantages • Treating of water flow might make

it possible to reuse water – less water consumption.

• Would probably appeal to SE segment.

• Useful in areas with poor water quality

Disadvantages • Changing water flow may cause a

need of redesign of the hydraulic system, due to pressure loss etcetera

• No disinfection of dishware • Disrupting water flow may cause

cavitations or other problems. • It will only disinfect parts of the

water, that later will be mixed and contaminated and partly treated again.

5-6. Inlet water treatment with UV light in contact with “inlet water container”.

The concepts are supposed to treat the water before entering the wash cycle. For this two options are available:

5 To change the material of the tank with a material transmitting UV-C and place lamp in contact with the tank

6 To treat the inlet water with a similar approach as described above. If there is approximately less than 3cm between source/bacteria and a 5W lamp is used, the needed tube has a length of 15cm and a diameter of 1cm. This is enough to disinfect a water flow of 4 l/min with 300J/m2

Advantages • Gives treatment to all the water used in

the dishwasher • Useful in countries with poor water

quality • Would probably appeal to SE segment. • The second option is possible without

any redesign work.

Disadvantages • Manufacturing problems due to

different material behaviour with UV transmitting plastic

• Manufacture plant may not support the new material.

• No disinfection of dishware • No treatment of the dirty water from

the dishware.

7. Sump treatment with UV lamp inside the sump.

An UV lamp is placed in the sump. In this way it is possible to both disinfect the flowing water and to disinfect the remaining soiled water within the sump. This may prevent bad smell coming from bacteria growth in the water.

Advantages • Could be possible to reuse water • Will disinfect the most

contaminated part of the dishwasher • Could be used during entire

program or after, to illuminate every hour to avoid bad smell and bacteria growth.

• Could appeal to SE

Disadvantages • May cause a different flow within

the sump. • No disinfection of dishware • Redesign of sump and filter needed


IV

8. Disinfect re-circulating water on the bottom of the tub

Re-circulated water could be disinfected by two lamps mounted on the bottom of the tub along its sides pointing to the bottom. This would allow to direct light at the bottom and at the lower basket.

Advantages • Possible to reuse water • Disinfect flat filter when not used • Could appeal to SE and AoS

Disadvantages • No disinfection of dishware • Rapid moving water with big treatment

area makes it hard to disinfect properly. • Could only treat flowing water <3cm

from lamp • Redesign of tub needed

9. UV zones in upper basket.

A dedicated zone in which UV light is directed towards delicate dishware that needs more disinfection. The zone could be visualized by using plastic inserts of different colours to inform user about the UV treatment area. The Lamp/tube can be assembled along the ceiling of the tub and it would be directed at the treatment area. Reflectors could be placed in basket to reflect the radiation towards the specified area.

Advantages • Possible to reuse existing lamp

socket. • Visible feature appealing to AoS • Increased disinfecting ability

appealing to SE

Disadvantages • Hard to reach areas, only one side of

the dishware will get a direct hit. • Redesign of tub may be needed

10. UV zone with UV enhanced optical fibre

Recently a new type of optical fibre has been developed which makes it possible to transmit UV light. This makes it possible to transport the light to any delicate ware that needs more disinfection. The connection between lamp and fibre could be similar as the one upper spray arm - water flow. With a flexible fibre the light spread can be rearranged by the user.

Advantages • “New” technology • Could be used within small spaces,

within the sump etcetera. • Appeal to AoS

Disadvantages • Expensive, fibre and diodes are

extremely expensive. • Possible risk that fibre wear out. • If movable fibre, risk that fibre

get tangled in a spray arm or baskets.

• Low intensity – Long exposure time

• Kill rate depends on the fibre output intensity. Larger fibre = more intensity, thus pretty low intensity.


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11. Sump disinfecting by UV lamp below the sump

The bottom part of the sump should be manufactured with a material that allows transmission of UV-C – like: quartz glass, EFEP, FEP. The UV lamp and reflector are placed underneath. This concept has similar pros and cons as the concept above.

Advantages • Possible reuse of water • Treat leftover water in bottom of sump. • Will disinfect the most contaminated

part of the dishwasher • Could be used during entire program or

after, to illuminate every hour to avoid bad smell and bacteria growth.

• Will not affect the flow or pressure

Disadvantages • No disinfection of dishware. • Redesign of sump needed, no space

for a lamp below sump.

12. Bottle sterilizer.

A vertical UV tube is placed in upper basket and ceiled with Quartz glass. The bottles are placed over the tube and disinfected from the inside.

Advantages • Could be used for other purposes as

well as Electrolux Water bottles. • Suitable with other Electrolux projects • Could appeal to SE and AoS • The method will also disinfect in some

way without that the bottle is placed.

Disadvantages • Bottle disinfecting may

compromise on cleaning • Electronics within basket

13. Central tube in lower basket.

A UV tube is placed in centre of the lower basket with a reflector pointing upwards. The tube has a connection to tub in some way to get electricity.

Advantages • With empty lower basket the tube is

covering most of the upper basket. • Clear and visible feature • Easy to exchange tube • Could appeal to SE and AoS

Disadvantages • Reduced space in lower basket • Difficult to implement electronics • The lamp needs a very robust

construction to deal with heavy loads from pots and pans etcetera.


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14. Germicidal UV LEDs.

A “new” invention is the germicidal UV LED. It could be used to disinfect by placing the LED wherever needed. The LED is though rather weak and has to be placed near the bacteria for a germicidal effect. The UV intensity is approximately 0,17W/m2 at a distance of 5cm. This means that the concept needs about 10 minutes to reach 100J/m2

at 5cm. Therefore it might be very costly to actually achieve any disinfection.

Advantages • New technology • Suitable for small areas. • Could appeal to AoS

Disadvantages • The LEDs are very expensive

compared to their UV output. • Low intensity UV source. • It will acquire some complicated

wiring

Extra1. Odour reducing sump disinfection.

One way to reduce the odour is to kill the bacteria that decompose left over soil by the filters. Therefore an UV lamp is place either above or below flat filter, targeting sump and filter.

Disadvantages • It will not disinfect the area above the flat filter if lamp is placed below or vice

verse. • The UV lamp will most likely only disinfect the first bacteria layer. This means that

living bacteria below the outer surfaces still exists and proceed with the decomposition.

Extra2. Ozonizer or an ozone generating UV lamp to remove odours.

The ozone generating device is connected to the existing fan in the dishwasher. Ozone could be used as a deodorizer and as a sterilizer.

Advantages • Do not affect plastics inside the tub. • Removes odour

Disadvantages • Ozone is hazardous and might

have a bad reputation • The ozone has a sharp smell

already at small concentration levels.


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Appendix 3 – Evaluation matrixes Concept elimination matrix

The concepts that received a good grade were marked with (Y)es and moved forward to next evaluation with a weighted matrix.


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Pughs weighted matrix


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Weight factor calculations


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Appendix 4 – Disinfection measurements Disinfection measurement with 4W UV tube or 5W PL-S lamp with an UV intensity of 9µW/cm2. For surface, flowing water, coil tubes and liquid treatment.

Surface treatment Bacteria killing dose? 100 J/m2 Lamp Intensity @ 1m? 9 uW/cm2 Distance lamp –bacteria? 50 cm Intensity at 50 cm: 0,36 W/m2 Time for killing dose: 278 s

Tube Bacteria killing dose: 100 J/m2 Lamp Intensity @ 1m: 9 uW/cm2 Distance lamp –bacteria: 2,5 cm Tube inner diameter 2 cm Tube length: 15 cm Water flow: 30 l/min Intensity @ 2,5cm: Tube volume

144 0,47

W/m2 dm3

Time for killing dose: 0,69 s Time in tube: 0,94 s Dose in tube: 135,6 J/m2

Coil tube maximize UV tube use Bacteria killing dose: 100 J/m2 Lamp Intensity @ 1m: 9 uW/cm2 Distance lamp –bacteria: 2 cm Tube inner diameter 1 cm Coil radius: 3 cm UV tube length: 15 cm Water flow: 30 l/min Tube area: 0,79 cm2 Tube length/coil lap: 18,8 cm Maximum exposed laps: 15 laps Max tube length: 283 cm Max tube volume: 222 cm3 2,2 litres Max time in tube: 4,4 s Intensity at coil distance: 100 W/m2 Max bacteria killing dose 444 J/m2 Time needed for killing dose: 1 s


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Coil Tube with Max 0,5 litre in tube: Bacteria killing dose: 100 J/m2 Lamp Intensity @ 1m: 9 uW/cm2 Distance lamp –bacteria: 2 cm Tube inner diameter 1 cm Coil radius: 3 cm UV tube length: 15 cm Water flow: 30 l/min Intensity at 2 cm: 225 W/m2 Max tube length: 63,7 cm Maximum exposed laps: 3,4 laps max water flow: 0,5 l/s Time in tube: 1 s Tube area: 0,8 cm2 Tube length/coil lap: 18,8 cm Intensity at coil distance: 100 W/m2 Time for killing dose: 1 s

Dose calculations in liquids Bacteria killing dose: 100 J/m2 Lamp Intensity @ 1m: 9 uW/cm2 Distance lamp – bacteria: 4 cm Lamp intensity @1m : 0,09 W/m2 Time needed for killing dose: 1,78 s Absorbation coefficient, alfa: 10 (white wine) Incident intensity, Eo at 0,04m: 56,3 W/m2 Liquid dept: 0,02 m New Intensity: 37,7 W/m2 Procental Intensity change: -33 % change New time for killing dose: 2,65 s

With absorbation coefficient according to table 1.


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Appendix 5 – Bacteria elimination doses

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